n = int(input())

names_dict = {}
family_names = []
first_names = []
for _ in range(n):
    s, t = input().split()
    family_names.append(s)
    first_names.append(t)
    if not s in names_dict:
        names_dict[s] = 0
    else:
        names_dict[s] += 1
    if not t in names_dict:
        names_dict[t] = 0
    else:
        names_dict[t] += 1

answer = "Yes"
for family_name, first_name in zip(family_names, first_names):
    if names_dict[family_name] >= 1 and names_dict[first_name] >= 1:
        answer = "No"
        break
print(answer)