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