#!/usr/bin/env python3
s = input()
t = 0
d = {t:0}
for i in s :
	t ^= 1 << (ord(i)-ord('a'))
	for j in range(26) :
		if (t^(1<<j)) in d :
			d[t] = min(d[t] if t in d else int(1e9),d[t^(1<<j)]+1)
print(d[t] if d[t] else 1)
