INF = 10 ** 9
s = input()
n = len(s)
l = [0] * (n + 1)
for i in range(n):
    l[i + 1] = l[i] ^ (1 << (ord(s[i]) - ord('a')))
dp = dict()
dp[0] = 0
for x in l[1:]:
    if x not in dp:
        dp[x] = INF
    for j in range(26):
        t = x ^ (1 << j)
        if t in dp:
            dp[x] = min(dp[x], dp[t] + 1)
ans = dp[l[-1]]
if ans == 0:
    print(1)
else:
    print(ans)
