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