#include<stdio.h>
lond int factorial(int n)
{
    if(n==o)
    {
        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;
}