import java.util.*;
public class digui{
	public static void main(String args[]){
		Scanner scanner =new Scanner(System.in);
		int number=scanner.nextInt();;
		System.out.println(dg(number));
		}

static int dg(int n){
	if(n==1||n==0){
		return 1;
}else if(n>1){	
		return n*dg(n-1)+(n-1)*dg(n-2);
}	
return 0;
}
}