import sys

S=sys.stdin.buffer.readline()
S=list(S)
A=[set() for i in range(26)]

for i in range(len(S)):
    if 0<=S[i]-97<26:
        A[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")