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