A TIMES B!

input/code.cpp: In function 'int main()':
input/code.cpp:124:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  124 |     for(int i=0; i<a.size(); i++) a[i] = sa[i]-'0';
      |                  ~^~~~~~~~~
input/code.cpp:125:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  125 |     for(int i=0; i<b.size(); i++) b[i] = sb[i]-'0';
      |                  ~^~~~~~~~~
input/code.cpp:134:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  134 |     for(int i=0; i<c.size()-1; i++){
      |                  ~^~~~~~~~~~~

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define pb push_back
#define VI vector<int>
#define AR(x) array<int, x>
#define MX vector<VI >
#define all(x) x.begin(), x.end()
#define IOS cin.tie(0)->sync_with_stdio(0)

using namespace std;

template<int MOD, int U> struct NTT {

    int B = 0;
    vector<vector<int> > w;
    vector<int> invbit;

    NTT(int B_) : B(B_), w(B_), invbit(1<<B_, 0) {
        
        w[B-1].resize(1<<(B-1));
        w[B-1][0] = 1;
        int u = pwr(U, (MOD-1)>>B);
        for(int i=1; i<(1<<(B-1)); i++) w[B-1][i] = (long long)w[B-1][i-1]*u%MOD;
        if(B>1) invbit[1] = 1;

        for(int b=B-2; b>=0; b--){
            int n = 1<<b, nn = 1<<(B-b-1);
            w[b].resize(n);
            for(int i=0; i<nn; i++){
                invbit[i] <<= 1;
                invbit[i+nn] = invbit[i]|1;
            }
            for(int i=0; i<n; i++) w[b][i] = w[b+1][2*i];
        }
    }

    int pwr(int a, int b){
        int p = 1;
        for(;b; b/=2){
            if(b&1) p = (long long)p*a%MOD;
            a = (long long)a*a%MOD;
        }
        return p;
    }
    
    int div(int x){
        int v0 = MOD, v1 = x, r0 = 0, r1 = 1;
        while(v1){
            int d = v0/v1;
            r0 -= d*r1; v0 -= d*v1;
            swap(v0, v1); swap(r0, r1);
        }
        return r0 < 0 ? r0+MOD : r0; 
    }

    void ntt(vector<int > &v, bool inv = 0){
        
        int n = v.size();
        int b = 0;
        while(1<<b < n) b++;
        
        n = 1<<b;
        v.resize(n, 0);

        int shift = B-b;
        for(int i=0; i<n; i++){
            if(i < invbit[i]>>shift) swap(v[i], v[invbit[i]>>shift]);
        }

        for(int r=0; r<b; r++){
            int rd = 1<<r;
            for(int i=0; i<n; i+=2*rd){
                for(int j=i; j<i+rd; j++){
                    long long tmp = (long long)w[r][j-i]*v[j+rd];
                    v[j+rd] = (v[j]-tmp)%MOD;
                    v[j] = (v[j]+tmp)%MOD;
                }
            }
        }

        for(int i=0; i<n; i++) if(v[i] < 0) v[i] += MOD;
        
        if(inv){
            int invn = div(n);
            reverse(v.begin()+1, v.end());
            for(int i=0; i<n; i++) v[i] = (long long)v[i]*invn%MOD;
        }
    }

    template<typename T> vector<T> conv(vector<T> &a, vector<T> &b, int n=0){
        
        if(n == 0) n = a.size()+b.size();

        vector<int> aa(n, 0), bb(n, 0);
        int za = a.size(), zb = b.size();
        for(int i=0; i<za; i++) aa[i] = a[i];
        for(int i=0; i<zb; i++) bb[i] = b[i];

        ntt(aa);
        ntt(bb);

        n = aa.size();
        for(int i=0; i<n; i++) aa[i] = (long long)aa[i]*bb[i]%MOD;

        ntt(aa, 1);
        
        vector<T> c(n, (T)0);
        for(int i=0; i<n; i++) c[i] = aa[i];

        return c;
    }
};

const int P = 998244353;

int main(){

    IOS;
    string sa, sb;
    
    cin >> sa >> sb;
    VI a(sa.size()), b(sb.size());
    for(int i=0; i<a.size(); i++) a[i] = sa[i]-'0';
    for(int i=0; i<b.size(); i++) b[i] = sb[i]-'0';
    reverse(all(a));
    reverse(all(b));


    NTT<P, 3> ntt(21);
    VI c = ntt.conv(a, b);
    
    c.resize(c.size()+100, 0);
    for(int i=0; i<c.size()-1; i++){
        c[i+1] += c[i]/10;
        c[i] %= 10;
    }

    while(!c.back()) c.pop_back();
    reverse(all(c));

    for(int i : c) cout << i;
    cout << '\n';

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED

Test 31

Verdict: ACCEPTED

Test 32

Verdict: ACCEPTED

Test 33

Verdict: ACCEPTED

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED

Test 36

Verdict: ACCEPTED

Test 37

Verdict: ACCEPTED

Test 38

Verdict: ACCEPTED

Test 39

Verdict: ACCEPTED

Test 40

Verdict: ACCEPTED

Test 41

Verdict: ACCEPTED

Test 42

Verdict: ACCEPTED

Test 43

Verdict: ACCEPTED

Test 44

Verdict: ACCEPTED

Test 45

Verdict: ACCEPTED

Test 46

Verdict: ACCEPTED

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: ACCEPTED

Test 51

Verdict: ACCEPTED

Test 52

Verdict: ACCEPTED

Test 53

Verdict: ACCEPTED

Test 54

Verdict: ACCEPTED

Test 55

Verdict: ACCEPTED

Test 56

Verdict: ACCEPTED

Test 57

Verdict: ACCEPTED

Test 58

Verdict: ACCEPTED

Test 59

Verdict: ACCEPTED

Test 60

Verdict: ACCEPTED

Test 61

Verdict: ACCEPTED

Test 62

Verdict: ACCEPTED

Test 63

Verdict: ACCEPTED

Test 64

Verdict: ACCEPTED

Test 65

Verdict: ACCEPTED