#include <bits/stdc++.h>

using namespace std;

void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

int main() {
    fast_io();
    int t;
    cin >> t;
    for (; t--;) {
        long long a, b;
        cin >> a >> b;
        if (a == b) {
            cout << 0 << "\n";
            continue;
        }
        vector<int> facts;
        for (long long i = 1; i * i <= b - a; i++) {
            facts.push_back(i);
            if (i != (b - a) / i) {
                facts.push_back((b - a) / i);
            }
        }
        sort(facts.begin(), facts.end());
        const long long INF = 1e18;
        long long ans = INF;
        for (long long f : facts) {
            long long x = f - a;
            if (x >= 0 && (b + x) % (a + x) == 0) {
                ans = min(ans, x);
            }
        }
        if (ans == INF) {
            cout << -1 << "\n";

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