#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" << endl;
    } else {
      int k = a / b;
      k = k + 1;
      cout << ((k * b) - a) << endl;
    }
  }
}
