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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int T;
    cin >> T;
    while(T--){
        ll a, b;
        cin >> a >> b;
        if(b % a == 0){
            cout << 0 << '\n';
            continue;
        }
        ll c = b / a;
        if(c == 1){
            cout << -1 << '\n';
            continue;
        }
        // c 倍以下は確定
        // A * k == B
        // (a + x) * k == (b + x)
        // a + (k - 1) * x == b
        // b - a == (k - 1) * x
        ll ans = -1;
        for(ll i = 1; i <= 50000; i++){
            if((b + i) % (a + i) == 0){
                ans = i;
                break;
            }
        }
        if(ans != -1){
            cout << ans << '\n';
            continue;
        }
        for(ll i = min(50000ll, c); i >= 2; i--){
            if((b - a * i) % (i - 1) == 0){
                ans = (b - a * i) / (i - 1);
                break;
            }
        }
        cout << ans << '\n';
    }
}