# !/usr/bin/ python3.8
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
from collections import Counter

N = int(readline())
m = map(int, read().split())
L = 112
graph = [[] for _ in range(L * L)]
for a, b, c, d in zip(m, m, m, m):
    x = L * a + b
    y = L * c + d
    graph[x].append(y)
    graph[y].append(x)

comp = [0] * (L * L)
ng = False
for i in range(L * L):
    if comp[i]:
        continue
    comp[i] = i
    Nv = 1
    Ne = 0
    stack = [i]
    while stack:
        v = stack.pop()
        for w in graph[v]:
            Ne += 1
            if comp[w]:
                continue
            comp[w] = i
            Nv += 1
            stack.append(w)
    Ne //= 2
    if Ne > Nv:
        ng = True
        break

print('NO' if ng else 'YES')