"""

最初と最後は空白→強制処理
それ以外は愚直に

"""
import sys
alp = "abcdefghijklmnopqrstuvwxyz"
dic = {}

for i in range(26):
    dic[alp[i]] = i

eve = [0] * 26
odd = [0] * 26

S = input()
if len(S) == 0:
    print ("NO")
    sys.exit()
for i in range(len(S)):

    if S[i] not in dic:
        continue

    if i % 2 == 0:
        eve[dic[S[i]]] += 1
    else:
        odd[dic[S[i]]] += 1

ans = "NO"
dic[" "] = float("inf")
for i in range(26):

    if eve[i] > 0 and odd[i] > 0:
        continue
    elif eve[i] > 1 or odd[i] > 2:
        ans = "Yes"
    elif eve[i]==1 and (S[-1] not in dic or dic[S[-1]] != i):
        ans = "Yes"
    elif odd[i]==1 and (S[-1] not in dic or dic[S[-1]] != i):
        ans = "Yes"

print (ans)