#!/usr/bin/env python3
s = input()
t = 0
d = {t:0}
for i in (ord(x)-ord('a') for x in s) :
	t ^= 1 << i
	c = d[t] if t in d else 1000000
	for j in range(26) :
		if t^(1<<j) in d :
			c = min(c,d[t^(1<<j)]+1)
	d[t] = c
print(d[t] if d[t] else 1)
