#include<stdio.h>
int factorial(int)
{
    if(n==0 || n==1)
    return 1;
    else
    return n*factorial(n-1);
}
int main()
{
    int n;
    int fact=1;
    scanf(%d,&n);
    if(n<0)
    {
        printf("Invalid Input");
        return 0;
    }
    else
    {
        printf("%d\n",factorial(n));
    }
    retun 0;
}