N=int(input())
A=[]
S,T={},{}
for i in range(N):
  a,b=input().split()
  A.append((a,b))
  if a not in S:
    S[a]=0
  S[a]+=1 
  if b not in T:
    T[b]=0
  T[b]+=1 
  
for a,b in A:
  f=0
  if a==b:
    if S[a]+T[b]==2:
      f=1
  if S[a]==1 and a not in T:
    f=1 
  if b not in S and T[b]==1:
    f=1 
  if f==0:
    print('No')
    exit()
print('Yes')