s = input()
n = len(s)
s = [ord(c)-ord('a') for c in s]
h = [0] * (n+1)
for i in range(1,n+1):
  h[i] = h[i-1] ^ (1<<s[i-1])
dp = {}
dp[0] = 0
bits = [2 ** i for i in range(26)]
for i in range(n):
  tmp = float("inf")
  for j in bits:
    try:
      tmp = min(dp[h[i+1]^j] + 1,tmp)
    except:
      pass
  try:
    e = dp[h[i+1]]
  except:
    e = float("inf")
  dp[h[i+1]] = min(tmp,e)
print(dp[h[n]] if dp[h[n]] != 0 else 1)