s = input()
n = len(s)
INF = 10**9

alph = "abcdefghijklmnopqrstuvwxyz"
to_int = {v: i for i, v in enumerate(alph)}
dp = {}
all_state = 0

for i in range(n):
    all_state ^= 1 << to_int[s[i]]
    if all_state not in dp:
        dp[all_state] = i + 1
    for j in range(26):
        bit = all_state ^ (1 << j)
        if bit in dp:
            dp[all_state] = min(dp[bit] + 1, dp[all_state])
    if bin(all_state).count("1") <= 1:
        dp[all_state] = 1
print(dp[all_state])