s = input()
N = len(s)
a = 0
dp = {}
dp[0] = 0
bits = [2 ** i for i in range(26)]

for c in s:
    a = a ^ bits[ord(c)-ord('a')]
    dp[a] = min(dp.get(a, N), min([dp.get(a ^ bit, N) for bit in bits]) + 1)

print(dp[a] if dp[a] != 0 else 1)
