from collections import Counter as co
from sys import exit
S=input()
L_l=list(S)
L_s=list(set(list(S)))
if ' ' in L_l:
  del L_l[L_l.index(' ')]
if ' ' in L_s:
  del L_s[L_s.index(' ')]
if len(L_s)==0:
  print('NO')
  exit()
C=co(L_l)
V=list(C.values())
V.sort()
if C[S[-1]]==1:
  if len(L_s)==1:
    print('NO')
    exit()
  elif V[1]==1:
    print('Yes')
    exit()
  else:
    del L_s[L_s.index(S[-1])]
    del L_l[L_l.index(S[-1])]
    S=S[0:len(S)-1]
space=list()
b=''
X=-1
Y=True
Z=True
for i in range(2**len(L_s)):
  X=-1
  Y=True
  Z=True
  space=list()
  space.append(' ')
  b=str(bin(i))
  b=b[2:len(b)]
  b='0000000000000000000000000000000'+b
  b=b[-len(L_s):]
  for j in range(len(L_s)):
    if b[j]=='0':
      space.append(L_s[j])
  for j in range(len(S)):
    if S[j] in space:
      if Y:
        if X==-1:
          True
        elif X%2==1:
          X=X+1
        else:
          Y=False
    else:
      if Y:
        if X==-1:
          X=1
        elif X%2==0:
          X=X+1
        else:
          Z=False
          break
      else:
        Z=False
        break
  if X>=2:
    if Z:
      print('Yes')
      exit()
print('NO')