#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int a, b;
    cin >> a >> b;
    if (a % b == 0)
      cout << "0" << endl;
    else
      cout << b - (a % b) << endl;
  }
}
