#include <bits/stdc++.h>
using namespace std;
long long d_sum(long long n) {
  long long res = 0;
  while (n) {
    res += n % 10;
    n /= 10;
  }
  return res;
}
void solve() {
  long long n, s;
  cin >> n >> s;
  long long old = n;
  long long sum = d_sum(n);
  if (sum <= s) {
    cout << "0\n";
    return;
  }
  long long cur = 1;
  while (sum > s) {
    cur *= 10;
    n /= 10;
    n++;
    sum = d_sum(n);
  }
  cout << n * cur - old << "\n";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long t;
  cin >> t;
  while (t--) solve();
}
