s = tuple(map(lambda c: ord(c)-ord('a'),input()))

from collections import defaultdict

dp = defaultdict(lambda: len(s))
dp[0] = 0


def it(x):
  for i in range(26):
    yield x ^ (1 << i)

v = 0
for c in s:
  v ^= 1 << c
  dp[v] = min(dp[v],min(dp[i] for i in it(v))+1)

print(dp[v] + (v == 0))