#include <bits/stdc++.h>
using namespace std;

#define FOR(i,l,r) for(int i = (int) (l);i < (int) (r);i++)
#define ALL(x) x.begin(),x.end()
template<typename T> bool chmax(T& a,const T& b){ return a < b ? (a = b,true) : false; }
template<typename T> bool chmin(T& a,const T& b){ return b < a ? (a = b,true) : false; }
typedef long long ll;

struct UnionFind{
	vector<int> par,rank;
	UnionFind(int n) :par(n + 1),rank(n + 1,1){
		for(int i = 1;i <= n;i++) par [i] = i;
	}
	int find(int x){
		return par [x] == x ? x : par [x] = find(par [x]);
	}
	bool connect(int x,int y){
		x = find(x);
		y = find(y);
		if(x == y) return false;
		if(rank [x] < rank [y]) swap(x,y);
		rank [x] += rank [x] == rank [y];
		par [y] = x;
		return true;
	}
	bool same(int x,int y){
		return find(x) == find(y);
	}
};

int N;
int A [10001];

int main()
{
	scanf("%d",&N);
	UnionFind uf(10000);
	FOR(i,0,N){
		int r1,c1,r2,c2;
		scanf("%d%d%d%d",&r1,&c1,&r2,&c2);
		int x = uf.find(r1 * 100 + c1),y = uf.find(r2 * 100 + c2);
		if(x == y){
			A [x]++;
		}
		else{
			uf.connect(x,y);
			A [uf.find(x)] = A [x] + A [y];
		}
	}

	FOR(i,1,10001){
		if(A [i] >= 2){
			printf("NO\n");
			return 0;
		}
	}

	printf("YES\n");

	return 0;
}