#pragma GCC optimize "O3,omit-frame-pointer,inline"
#pragma GCC push_options
#pragma GCC optimize ("unroll-loops")
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

signed main () {
  std::ios::sync_with_stdio(false); std::cin.tie(0);
  int t;
  cin >> t;

  while (t--) {
    int a, b;
    cin >> a >> b;
    if (b % a == 0) {
     cout << 0 << endl;
     continue;
    }

    int n = b - a;

    int ans = 2e9;
    for (int c = 1; c * c <= n; c++) {
      if (n % c == 0) {
        int x = c;
        int y = n / c;
        if (x - a >= 0) ans = min(ans, x - a);
        if (y - a >= 0) ans = min(ans, y - a);
      }
    }

    cout << (ans == 2e9 ? -1 : ans) << endl;
  }

  return 0;  
}