codegolf.a.factorial

import java.math.*;
public class A {
    public static void main(String[]a) {
        System.out.print(a.length<1?1:f(new Long(a[0])));
    }
    static BigInteger f(long n) {
        return n<1?BigInteger.ONE:BigInteger.valueOf(n).multiply(f(n-1));
    }
}