#include <bits/stdc++.h>
using namespace std;
vector<string> split(const string& s, char c) {
  vector<string> v;
  stringstream ss(s);
  string x;
  while (getline(ss, x, c)) {
    v.emplace_back(x);
  }
  return move(v);
}
template <typename T, typename... Args>
inline string arrStr(T arr, int n) {
  stringstream s;
  s << "[";
  for (int i = 0; i < n - 1; i++) {
    s << arr[i] << ",";
  }
  s << arr[n - 1] << "]";
  return s.str();
}
template <typename T>
inline void __evars_out_var(vector<T> val) {
  cerr << arrStr(val, val.size());
}
template <typename T>
inline void __evars_out_var(T* val) {
  cerr << arrStr(val, 10);
}
template <typename T>
inline void __evars_out_var(T val) {
  cerr << val;
}
inline void __evars(vector<string>::iterator it) { cerr << "\n"; }
template <typename T, typename... Args>
inline void __evars(vector<string>::iterator it, T a, Args... args) {
  cerr << "[" << it->substr((*it)[0] == ' ', it->length()) << ": ";
  __evars_out_var(a);
  cerr << "]"
       << " ";
  __evars(++it, args...);
}
int main(int argc, char* const argv[]) {
  ios_base ::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int t;
  cin >> t;
  while (t--) {
    int a, b;
    cin >> a >> b;
    cout << (b - a % b) % b << "\n";
  }
  return 0;
}
