八皇后

#include <bits/stdc++.h>
#define ll long long
using namespace std;
bool vis[30] = {false};
bool lr[30] = {false};
bool fr[30] = {false};

ll cnt=0;
int n;

bool mark(int x, int y){
	if(vis[y] || lr[y-x+n] || fr[x+y]){
		return false;
	}
	return true;
}

void dfs(int x){
	if(x==n){
		cnt++;
		return;
	}
	for(int i=1; i<=n; i++){
		if(!mark(x,i)){
			continue;
		}
		vis[i] = true;
		lr[i-x+n] = true;
		fr[x+i] = true;
		dfs(x+1);
		 
		vis[i] = false;
		lr[i-x+n] = false;
		fr[x+i] = false;
	}
	return;
}

int main(){
	cin >> n;
	dfs(0);
	cout << cnt;
	return 0;
}