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