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