#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  long long a, b;
  for (int i = 0; i < t; i++) {
    cin >> a >> b;
    if (a % b == 0) {
      cout << "0"
           << "\n";
    } else {
      cout << (b - (a % b)) << "\n";
    }
  }
}
