#include <bits/stdc++.h>
using namespace std;
int sum(long long n) {
  int res = 0;
  while (n > 0) {
    res += n % 10;
    n /= 10;
  }
  return res;
}
void solve() {
  long long n, s;
  cin >> n >> s;
  if (sum(n) <= s) {
    cout << "0" << endl;
    return;
  }
  long long ans = 0;
  long long pw = 1;
  for (int i = 0; i < 18; i++) {
    int digit = (n / pw) % 10;
    long long add = pw * ((10 - digit) % 10);
    n += add;
    ans += add;
    if (sum(n) <= s) {
      break;
    }
    pw *= 10;
  }
  cout << ans << endl;
}
int main() {
  long long test = 1;
  cin >> test;
  while (test--) {
    solve();
  }
  return 0;
}
