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

vector<long long> divisor(const long long &n)
{
    vector<long long> ret;
    for (long long i = 1; i * i <= n; i++)
    {
        if (n % i == 0)
        {
            ret.push_back(i);
            if (i * i != n)
                ret.push_back(n / i);
        }
    }
    sort(ret.begin(), ret.end()); // 昇順に並べる
    return ret;
}

int main()
{
    int T;
    cin >> T;
    for (int i = 0; i < T; i++)
    {
        // vector<long long> vec;
        long long A, B;
        cin >> A >> B;
        vector<long long> vec = divisor(B - A);
        bool nasi = true;
        if (A == B)
        {
            cout << 0 << "\n";
            continue;
        }
        for (auto v : vec)
        {

            if (v >= A)
            {
                cout << v - A << "\n";
                nasi = false;
                break;
            }
        }
        if (nasi)
        {
            cout << -1 << "\n";
        }
    }
}