#  --*-coding:utf-8-*--

import math

def f(str):
    s = {}
    s[0] = 0
    pat = 0

    for c in str:
        pat ^= 2**(ord(c)-97)
        s[pat] = min(
            min(s.get(pat^2**i, math.inf) + 1 for i in range(26)),
            s.get(pat, math.inf))

    if pat == 0:
        return 1

    return s[pat]
            

def test():
    assert f('aabxyyzz') == 2
    assert f('byebye') == 1
    assert f('abcdefghijklmnopqrstuvwxyz') == 26
    assert f('abcabcxabcx') == 3


def main():
    str = input()
    print(f(str))


if __name__ == '__main__':
    main()
