#include<stdio.h>
long int factorial(int v)
{
    if(v==0)
    {
        return 1;
    }
    else
    {
        return n* factorial(n-1);
    }
}
int main()
{
    int num;
    scanf("%d",&num);
    if(num < 0)
    {
        printf("Invalid input");
        return 0;
    }
    long int result = factorial(num);
    printf("%ld",result);
    return 0;
}