class Nfakulte 
   
  { 
  	public static void main(String[] args)  
  	{ 
  		int n; 
  		int s; 
  		int i; 
  		 
  		n = Integer.parseInt(args[0]); 
  		s = 1; 
  		i = 2; 
  		 
  		while (i <= n) 
  		{ 
  			s = s*i; 
  			i = i+2; 
  		} 
  		System.out.println(s); 
  	} 
  }