#include<stdio.h>
int main(){
    int n, fact=1;
    scanf("%d",&n);
    
    if(n<0){
        printf("invalid input");
 } else   {
        for (int i=1;i<=n;i+
    +)  
        fact*=i;
        printf("%d",fact);
        
        }
returm 0;
    
    
}