func_code_string: #include <bits/stdc++.h>   using namespace std;   unsigned long long dsum(unsigned long long n) {     unsigned long long res = 0;     while (n) {       res += n % 10;       n /= 10;     }     return res;   }   int main() {     unsigned long long n, s;     cin >> n >> s;     unsigned long long dif = n - dsum(n);     if (dif < s)       cout << 0 << endl;     else {       unsigned long long l = 1, h = n;       while (h - l > 0) {         unsigned long long mid = l + (h - l) / 2;         unsigned long long x = dsum(mid);         dif = mid - x;         if (dif < s) {           l = mid + 1;         } else           h = mid;       }       if (n - dsum(l) >= s) l--;       cout << n - l << endl;     }   }   