using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Globalization;
using System.Diagnostics;
using static System.Console;
using Pair = System.Collections.Generic.KeyValuePair<int, int>;

//閉路があるかないか
class Program
{
    static void Main()
    {
        SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        new Program().Solve();
        Out.Flush();
    }
    Scanner cin = new Scanner();
    readonly int[] dd = { 0, 1, 0, -1, 0 };
    readonly int mod = 1000000007;
    readonly string alfa = "abcdefghijklmnopqrstuvwxyz";

    bool[] J;
    List<int>[] G;
    bool flag;
    void Solve()
    {
        int N = cin.Nextint;
        G = Enumerable.Range(0, 10010).Select(i => new List<int>()).ToArray();
        for (int i = 0; i < N; i++)
        {
            var C = cin.Scanint.Select(k => k - 1).ToArray();
            G[C[0] * 100 + C[1]].Add(C[2] * 100 + C[3]);
            G[C[2] * 100 + C[3]].Add(C[0] * 100 + C[1]);
        }
        for (int i = 0; i < 10010; i++)
        {
            J = new bool[10010];
            Dfs(i, -1);
            if (flag) break;
        }
        WriteLine((flag) ? "NO" : "YES");
    }
    void Dfs(int now, int before)
    {
        if(J[now])
        {
            flag = true;
            return;
        }
        J[now] = true;
        foreach (var v in G[now])
        {
            if (v == before) continue;
            Dfs(v, now);
        }
    }
}

class Scanner
{
    string[] s; int i;
    char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] Scan { get { return ReadLine().Split(); } }
    public int[] Scanint { get { return Array.ConvertAll(Scan, int.Parse); } }
    public long[] Scanlong { get { return Array.ConvertAll(Scan, long.Parse); } }
    public double[] Scandouble { get { return Array.ConvertAll(Scan, double.Parse); } }
    public string Next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return Next;
        }
    }
    public int Nextint { get { return int.Parse(Next); } }
    public long Nextlong { get { return long.Parse(Next); } }
    public double Nextdouble { get { return double.Parse(Next); } }
}