#include<bits/stdc++.h>
using namespace std;
long long a,b;
long long minzhi(long long n){
	if(n%2==0)return 2;
	for(long long i=3;i*i<=n;i+=2)
		if(n%i==0)return i;
	return n;
}
int main(){
    cin>>a>>b;
    long long x=__gcd(a,b);
    if(x==1){cout<<-1;return 0;}
    cout<<x/minzhi(x);
    return 0;
}