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