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