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