#include<stdio.h>
int main (){
    int n;
    long;long; factorial=1;
    scanf("%d0",&n);
    if(n<0||n>20)
{
    printf("Invalid input");
}
else{
    for(int i-1;i<-n;i++)
 {
     factorial-i;
 }
 printf("%d",factorial);
}
return 0;
}