from collections import Counter

# 入力
N = int(input())
names = []
all_names = []

for _ in range(N):
    s, t = input().split()
    names.append((s, t))
    all_names.append(s)
    all_names.append(t)

# 统计所有姓和名的出现次数
count = Counter(all_names)

# 对每个人检查：是否有至少一个唯一的（即出现1次的）名字
for s, t in names:
    if count[s] > 1 and count[t] > 1:
        print("No")
        break
else:
    print("Yes")