A TIMES B!

input/code.cpp: In function 'int main()':
input/code.cpp:65:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   65 |     scanf("%s%s", s1, s2);
      |     ~~~~~^~~~~~~~~~~~~~~~

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;

int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch <= '9' && ch >= '0') {
    x = 10 * x + ch - '0';
    ch = getchar();
  }
  return x * f;
}

void print(int x) {
  if (x < 0) putchar('-'), x = -x;
  if (x >= 10) print(x / 10);
  putchar(x % 10 + '0');
}

constexpr int N = 4000010, P = 998244353;
int x1[N], x2[N], r[N];
char s1[N], s2[N];

int QuickPow(int x, int y) {
  int res(1);
  while (y) {
    if (y & 1) res = 1ll * res * x % P;
    x = 1ll * x * x % P;
    y >>= 1;
  }
  return res;
}

void NTT(int *x, int lim, int opt) {
  int i, j, k, m, gn, g, tmp;
  for (i = 0; i < lim; ++i)
    if (r[i] < i) swap(x[i], x[r[i]]);
  for (m = 2; m <= lim; m <<= 1) {
    k = m >> 1;
    gn = QuickPow(3, (P - 1) / m);
    for (i = 0; i < lim; i += m) {
      g = 1;
      for (j = 0; j < k; ++j, g = 1ll * g * gn % P) {
        tmp = 1ll * x[i + j + k] * g % P;
        x[i + j + k] = (x[i + j] - tmp + P) % P;
        x[i + j] = (x[i + j] + tmp) % P;
      }
    }
  }
  if (opt == -1) {
    reverse(x + 1, x + lim);
    int inv = QuickPow(lim, P - 2);
    for (i = 0; i < lim; ++i) x[i] = 1ll * x[i] * inv % P;
  }
}

int main()
{
    // Test();
    scanf("%s%s", s1, s2);
    int l1 = strlen(s1), l2 = strlen(s2);
    int lim = 1;
    while(lim < l1*2 || lim < l2*2)
        lim <<= 1;

    for(int i=0; i < l1; i++)
        x1[i] = s1[l1 - i - 1] - '0';
    for(int i=0; i < l2; i++)
        x2[i] = s2[l2 - i - 1] - '0';
    for (int i = 0; i < lim; ++i) 
        r[i] = (i & 1) * (lim >> 1) + (r[i >> 1] >> 1);
    NTT(x1, lim, 1);
    NTT(x2, lim, 1);
    for (int i = 0; i < lim; ++i) 
        x1[i] = 1ll * x1[i] * x2[i] % P;
    NTT(x1, lim, -1);

    int len(0);
    for (int i = 0; i < lim; ++i) {
        if (x1[i] >= 10) 
        {
            len = i + 1;
            x1[i + 1] += x1[i] / 10;
            x1[i] %= 10;
        }
        if (x1[i]) len = max(len, i);
    }
    while (x1[len] >= 10) 
    {
        x1[len + 1] += x1[len] / 10;
        x1[len] %= 10;
        len++;
    }
    for (int i = len; ~i; --i) 
        putchar(x1[i] + '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