#include <iostream>
#include <vector>
using namespace std;
using ll = long long;

bool judges(ll X){
    vector<ll> divs;
    ll xcpy = X;
    for (ll i = 2; i * i <= X; i++){
        while (xcpy % i == 0){
            divs.push_back(i);
            xcpy /= i;
        }
    }
    if (xcpy != 1){
        divs.push_back(xcpy);
    }
    if (divs.size() != 4){
        return false;
    }
    if (divs[0] == 2){
        return false;
    }
    else if (!(divs[0] == divs[1] && divs[1] != divs[2] && divs[2] != divs[3])){
        return false;
    }
    return true;
}

int main(){
    ll L, R;
    cin >> L >> R;

    for (ll i = L; i <= R; i++){
        if (judges(i)){
            cout << i << endl;
            return 0;
        }
    }
    cout << -1 << endl;
}