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

int main() {
	int t;
	cin>>t;
	while(t--)
	{
	    int x,y;
	    cin>>x>>y;
	    int cnt=0;
	    for(int i=2;i<=100;i++)
	    {
	        if(i%x!=0 && i%y!=0)
	        {
	            cout<<i;
	            cnt=1;
	            break;
	        }
	        else
	            continue;
	    }
	    if(cnt==0)
	        cout<<-1<<endl;
	   else
	        cout<<endl;
	}

}