#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);
    if(n<0){
        printf("Invalid input\n")
    }
    else{
        printf("%d\n",factorial(n));
    }
    
return 0;
}