#include <bits/stdc++.h>
using namespace std;
using ll = long long;

vector<ll> Divisor(ll n) {
  vector<ll> r;
  for(ll i = 1; i * i <= n; i++) {
    if(n % i == 0) {
      r.emplace_back(i);
      if(i * i != n) { r.emplace_back(n / i); }
    }
  }
  ranges::sort(r);
  return r;
}

void solve() {
  ll A, B;
  cin >> A >> B;

  ll ans = -1;
  for(auto &i : Divisor(B - A)) {
    if(i >= A) {
      ans = i - A;
      break;
    }
  }

  if(B % A == 0) { ans = 0; }

  cout << ans << "\n";
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll t;
  cin >> t;
  while(t--) { solve(); }
}