text: #include<stdio.h>
  #include<stdlib.h>
  
  int fac(int n) {
  	if(n>>1)
  		return n*fac(n-1);
  	return 1;
  }
  
  int main(int argc,char *argv[]) {
  	if(argc!=2)	{
  		printf("[USAGE] %s [int]\n",argv[0]);
  		exit(-1);
  	}
  	int n=atoi(argv[1]);
  	printf("[FACTORIAL(%d)] %d\n",n,fac(n));
  	return 0;
  }
  