C++ :

#include<bits/stdc++.h>
using namespace std;
int n;
int xinfeng(int n){
	if(n==1)return 0;
	else if(n==2)return 1;
	else return (n-1)*(xinfeng(n-1)+xinfeng(n-2));
}
int main(){
	cin>>n;
	cout<<xinfeng(n);
    return 0;
}

Java :

import java.util.Scanner;

public class Main {
	static int d[] = new int[13];
	static int xinfeng(int n) {
		if(n==1) d[n]=0;
		else if(n==2) d[n]=1;
		else if(n>2) d[n] = (n-1)*(xinfeng(n-1)+xinfeng(n-2));
		return d[n];
	}
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		System.out.println(xinfeng(n));
		sc.close();
	}

}