#include <stdio.h>
#include <stdlib.h>

double factorial(int n)
{
  if(n<=0)
    return(1.0);
  else
    return(n*factorial2(n-1));
}

double factorial2(int n)
{
  double result;

  result=1;
  while(n>0)
  {
    result *= n--;
  }
  return(result);
}


int main(int argc, char *argv[])
{
  int n;

  n= atoi(argv[1]);
  printf("fac(%d)=%e\n", n, factorial(n));   
  return(0);
}