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

#define rep(i, N) for (int i = 0; i < (int)N; i++)
#define INF 1000000001

int main() {
  int T;
  cin >> T;
  rep(i, T) {
    int A, B;
    cin >> A >> B;
    int X = INF;
    if (B - A == 0)
      X = 0;
    else
      for (int j = 1; j*j <= B - A; j++) {
	int c = B - A;
	if (c % j == 0) {
	  if (c / j - A >= 0)
	    X = min(c / j - A, X);
	  if (j - A >= 0)
	    X = min(j - A, X);
	}
      }
    if (X == INF)
      cout << -1 << endl;
    else
      cout << X << endl;
  }
  return 0;
}