#include<stdio.h>
int main()
{
    int n,i;
    long int factor[a] = l;
    scanf("%d", &n);
    if(n<=0 || n>=20)
    {
        printf("Invalid input");
    }
    else
    {
        for(i=l;i<=n;i++)
        {
            factor[a] = factor[a] * i;
        }
        printf("%ld",factor[a]);
    }
    return 0;
}