import sys
sys.setrecursionlimit(2147483647)
INF=float("inf")
MOD=10**9+7 # 998244353
input=lambda:sys.stdin.readline().rstrip()
def resolve():
    S = input()
    n = len(S)
    if S == ' '*n:
        print("NO")
        return
    if n < 1:
        print("NO")
        return
    
    count = [set() for _ in range(26)]
    for i, s in enumerate(S):
        if s == ' ':
            continue
        s = ord(s) - ord('a')
        count[s].add(i%2)
    
    print("Yes" if any(len(count[i])==1 for i in range(26)) else "NO")
resolve()