#include <bits/stdc++.h>
using namespace std;
int main()
{
    int t;
    cin >> t;
    for (int i = 0; i < t; i++)
    {
        int a, b, n, lcd=0;
        cin >> a >> b;
        n = 2;
        while (1)
        {
            if ((a % n == 0) && (b % n == 0))
            {
                lcd = n;
                break;
            }
            ++n;
        }
        if (lcd != 0)
        {
            cout << lcd << endl;
        }
        else cout<<"-1"<<endl;
    }

    return 0;
}