import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

S=input().strip()
A=[set() for i in range(26)]

for i in range(len(S)):
    if 0<=ord(S[i])-97<26:
        A[ord(S[i])-97].add(i%2)

if len(S)<=1:
    print("NO")
    sys.exit()
    

for a in A:
    if len(a)==1:
        print("Yes")
        break
else:
    print("NO")