#include<bits/stdc++.h>
using namespace std;
void solve()
{
    int n,m; cin>>n>>m;
    int a=min(n,m);
    //int b=sqrt(a);
    for(int i=2;i<=a;i++)
    {
        if(n%i==0 && m%i==0)
        {
            cout<<i<<endl;
            return;
        }
    }
    //if(max(n,m)%a==0 && a!=1) {cout<<a<<endl; return;}
    cout<<-1<<endl;
}
int main()
{
    int t; cin>>t; while(t--) solve();
}