import sys
from collections import defaultdict as dd
input = sys.stdin.readline
S = list(input())[: -1]
N = len(S)
cs = [0] * (N + 1)
a = ord("a")
for i in range(N):
  cs[i + 1] = cs[i] ^ (1 << (ord(S[i]) - a))
#print(cs)
d = dd(lambda: N + 1)
for i in range(N, -1, -1): d[cs[i]] = i

x = N
res = 0
while x:
  y = x - 1
  for i in range(26): y = min(y, d[cs[x] ^ (1 << i)])
  y = min(y, d[cs[x]])
  x = y
  res += 1
print(res)