from collections import defaultdict

s = input()

n = len(s)
inf = 10**6
d = defaultdict(lambda : inf)
d[0] = 0

a = ord('a')
now = 0
for i in range(n):
    si = ord(s[i]) - a
    now = now^(1<<si)
    for j in range(26):
        d[now] = min(d[now], 1+d[now^(1<<j)])

print(max(1,d[now]))