#include <iostream>
#include <climits>

using namespace std;

int main()
{
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int T, i, A, B, j, min;
    cin >> T;
    for (i = 0; i != T; ++i)
    {
        min = INT_MAX;
        cin >> A >> B;
        const int gap = B - A;
        if (gap == 0)
        {
            cout << "0\n";
            continue;
        }

        for (j = 1; j * j <= gap; ++j)
            if (gap % j == 0)
            {
                if (j >= A)
                {
                    if (j - A < min)
                        min = j - A;
                }
                else if (gap / j >= A)
                {
                    if (gap / j - A < min)
                        min = gap / j - A;
                }
            }

        if (min == INT_MAX) cout << "-1\n";
        else cout << min << '\n';
    }

    return 0;
}