from itertools import accumulate
from operator import xor

s = tuple(map(lambda c: 1 << (ord(c)-ord('a')),input()))
L = len(s)
dp = dict()
dp[0] = 0

for v in accumulate(s, xor):
  dp[v] = min(dp.get(v,L), min(dp.get(v ^ (1 << i), L) for i in range(26))+1)

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