// editor2
#include<stdio.h>
unsigned long long factorial(int n)
{
    if(n==0||n==1)
    return 1;
    else
    return n*factorial(n-1);
    
}
int main()
{
    int num;
    printf("%d",n*factorial(n-1));
    scanf("%d",&num);
    if(num<0)
    {
        
       printf("Invalid Input");
    
    }
}