#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
using ll = long long;

constexpr int iINF = 1'000'000'000;
constexpr ll llINF = 1'000'000'000'000'000'000;

vector<int> divisors (int x) {
    vector<int> res;
    for (int i = 1; 1LL * i * i <= x; i++) {
        if (x % i == 0) res.push_back(i);
        if (1LL * i * i == x) continue;
        res.push_back(x / i);
    }

    sort(res.begin(), res.end());
    return res;
}

void solve (int A, int B) {
    if (A == 1) {
        cout << 0 << "\n";
        return;
    }
    if (A == B) {
        cout << 0 << "\n";
        return;
    }

    auto d = divisors(B - A);

    int ans = -1;
    for (auto v : d) {
        if (A <= v) {
            int candi = v - A;
            if ((B + candi) % (A + candi) == 0) {
                ans = candi;
                break;
            }
        }
    }

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

int main () {
    int T; cin >> T;
    for (int i = 0; i < T; i++) {
        int A, B; cin >> A >> B;
        solve(A, B);
    }
}