#include <bits/stdc++.h>   using namespace std;   int main() {     long long int t;     cin >> t;     while (t--) {       long long int a, b;       cin >> a >> b;       long long int x;       x = a % b;       if (x == 0)         cout << x << endl;       else {         long long int r = a / b;         long long int res = (r + 1) * b - a;         cout << res << endl;       }     }   }   