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