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