#include<iostream>
#include<bits/stdc++.h>
using namespace std;
#define ll long long int


void solve(){
    int n, m;
    cin>>n>>m;

    int mn = min(n, m);

    for(int i=2;i<=mn;i++){
        if(n%i==0 && m%i==0){
            cout<<i<<endl;
            return;
        }
    }

    cout<<-1<<endl;
}

int main(){

    int t;
    cin>>t;
    while(t--){
        solve();
    }

    return 0;
}