A TIMES B!

#include <iostream>
#include <string>
#include <vector>
using namespace std;

const long long MOD = 998244353, G = 3;

long long pw(long long b, long long e) {
    long long r = 1;
    b %= MOD;
    while (e) {
        if (e & 1) r = r * b % MOD;
        b = b * b % MOD;
        e >>= 1;
    }
    return r;
}

void ntt(vector<long long>& a, bool inv) {
    int n = a.size();
    for (int i = 1, j = 0; i < n; i++) {
        int bit = n >> 1;
        for (; j & bit; bit >>= 1) j ^= bit;
        j ^= bit;
        if (i < j) swap(a[i], a[j]);
    }
    for (int len = 2; len <= n; len <<= 1) {
        long long w = pw(G, (MOD - 1) / len);
        if (inv) w = pw(w, MOD - 2);
        for (int i = 0; i < n; i += len) {
            long long wn = 1;
            for (int j = 0; j < len / 2; j++) {
                long long u = a[i + j], v = a[i + j + len / 2] * wn % MOD;
                a[i + j] = u + v < MOD ? u + v : u + v - MOD;
                a[i + j + len / 2] = u - v >= 0 ? u - v : u - v + MOD;
                wn = wn * w % MOD;
            }
        }
    }
    if (inv) {
        long long ni = pw(n, MOD - 2);
        for (auto& x : a) x = x * ni % MOD;
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    string s, t;
    cin >> s >> t;
    int n = 1;
    while (n < (int)(s.size() + t.size())) n <<= 1;
    vector<long long> a(n), b(n);
    for (int i = 0; i < (int)s.size(); i++) a[i] = s[s.size() - 1 - i] - '0';
    for (int i = 0; i < (int)t.size(); i++) b[i] = t[t.size() - 1 - i] - '0';
    ntt(a, false);
    ntt(b, false);
    for (int i = 0; i < n; i++) a[i] = a[i] * b[i] % MOD;
    ntt(a, true);
    long long carry = 0;
    for (int i = 0; i < n; i++) {
        a[i] += carry;
        carry = a[i] / 10;
        a[i] %= 10;
    }
    int k = n - 1;
    while (k > 0 && a[k] == 0) k--;
    string r;
    for (int i = k; i >= 0; i--) r += char('0' + a[i]);
    cout << r << "\n";
}

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