#include <iostream>
#include <fstream>

using namespace std;

int main (){

    ifstream fin("fact.in");
    ofstream out("fact.out");

    long long int n;

    fin >> n;

    if(n > 0){
        unsigned long long int i = 1, p = 1;
        while(i <= n){

            p *= i;++i;
        }
            out << p;
    }
    else
        out << "-1";

}