s = input()

n = len(s)
inf = 10**6
dp = [inf] * (2**26)
dp[0] = 0

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

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