#include <iostream>
using namespace std;

int main(){
    int n;
    cin >> n;
    int p = 1,
        gasit = 0;


    while( n ){
        if(n % 2 == 1)
        {
            p *= n%10;
            gasit = 1;
        }
        n /= 10;
    }

    if(!gasit)
        p = -1;


    cout << p << endl;

    return 0;
}