A TIMES B!

input/code.cpp: In function 'void Test()':
input/code.cpp:66:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   66 |     freopen("temp\\in.txt", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
input/code.cpp: In function 'int main()':
input/code.cpp:75:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   75 |     scanf("%s%s", s1, s2);
      |     ~~~~~^~~~~~~~~~~~~~~~

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=1048580;
const double PI = acos(-1.0);

struct Complex {
    double x, y;
    Complex(double x_ = 0.0, double y_ = 0.0) {
        x = x_;
        y = y_;
    }
    Complex operator - (const Complex& A)const {
        return Complex(x - A.x, y - A.y);
    }
    Complex operator + (const Complex& A)const {
        return Complex(x + A.x, y + A.y);
    }
    Complex operator * (const Complex& A)const {
        return Complex(x*A.x - y*A.y, x*A.y + y*A.x);
    }
};

void Change(Complex y[], int len)
{
    int i, j, k;
    for(i = 1, j = len/2; i < len - 1; i++)
    {
        if(i < j) swap(y[i], y[j]);
        k = len/2;
        while(j >= k)
        {
            j -= k;
            k /= 2;
        }
        if(j < k) j += k;
    }
}

void FFT(Complex y[], int len, int on)
{
    Change(y, len);
    for(int h = 2; h <= len; h<<=1)
    {
        Complex wn(cos(-on*2*PI/h), sin(-on*2*PI/h));
        for(int j = 0; j < len; j+=h)
        {
            Complex w(1, 0);
            for(int k = j; k < j + h/2; k++)
            {
                Complex u = y[k];
                Complex t = w*y[k + h/2];
                y[k] = u + t;
                y[k+h/2] = u - t;
                w = w * wn;
            }
        }
    }
    if(on == -1)
        for(int i=0; i<len; i++)
            y[i].x /= len;
}

void Test()
{
    freopen("temp\\in.txt", "r", stdin);
}

Complex x1[N], x2[N];
char s1[N], s2[N];
int sum[N];
int main()
{
    // Test();
    scanf("%s%s", s1, s2);
    int l1 = strlen(s1), l2 = strlen(s2);
    int len = 1;
    while(len < l1*2 || len < l2*2)
        len <<= 1;

    for(int i=0; i<l1; i++)
        x1[i] = Complex(s1[l1-1-i] - '0', 0);
    for(int i=l1; i<len; i++)
        x1[i] = Complex(0, 0);
    for(int i=0; i<l2; i++)
        x2[i] = Complex(s2[l2-1-i] - '0', 0);
    for(int i=l2; i<len; i++)
        x2[i] = Complex(0, 0);
    
    FFT(x1, len, 1);
    FFT(x2, len, 1);
    for(int i=0; i<len; i++)
        x1[i] = x1[i] * x2[i];
    FFT(x1, len, -1);

    for(int i=0; i<len; i++)
        sum[i] = (int)(x1[i].x + 0.5);
    for(int i=0; i<len; i++)
    {
        sum[i+1] += sum[i]/10;
        sum[i] %= 10;
    }
    len = l1 + l2 - 1;
    while(sum[len] <= 0 && len > 0)
        len --;
    for(int i=len; i>=0; i--)
        putchar(sum[i]+'0');

    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: RUNTIME ERROR

Test 62

Verdict: RUNTIME ERROR

Test 63

Verdict: RUNTIME ERROR

Test 64

Verdict: RUNTIME ERROR

Test 65

Verdict: RUNTIME ERROR