// editor2
#include<stdio.h>
int factoria(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;
}