// editor1
#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");
    }
    elsde{
        printf("%d",factorial(n));
    }
    return 0;
}