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