#include<bits/stdc++.h>
#define int long long
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
using namespace std;
template<typename T>istream&operator>>(istream&I,vector<T>&v){for(auto&i:v)I>>i;return I;}
template<typename T>ostream&operator<<(ostream&O,vector<T>&v){for(auto&i:v)O<<i<<' ';return O;}
namespace AC{
vector<array<int,2>>g[110][110];
int ver,edg;
bool vis[110][110];
void dfs(int x,int y){
	if(vis[x][y])return;
	vis[x][y]=1;
	ver++,edg+=g[x][y].size();
	for(auto&i:g[x][y])dfs(i[0],i[1]);
}
void solve(){
	for(int i=0;i<110;i++)for(int j=0;j<110;j++)g[i][j].clear(),vis[i][j]=0;
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		int x1,y1,x2,y2;
		cin>>x1>>y1>>x2>>y2;
		g[x1][y1].push_back({x2,y2});
		g[x2][y2].push_back({x1,y1});
	}
	for(int i=0;i<110;i++)for(int j=0;j<110;j++)if(g[i][j].size()&&!vis[i][j]){
		ver=edg=0;
		dfs(i,j);
		edg/=2;
		if(ver<edg){
			cout<<"NO"<<endl;
			return;
		}
	}
	cout<<"YES"<<endl;
}
}
signed main(){
	int t=1;
	//cin>>t;
	while(t--)AC::solve();
}