def main():
    S = input()
    a = {j: i for i, j in enumerate('abcdefghijklmnopqrstuvwxyz')}
    S = [a[i] for i in S]

    parity = 0
    dict_parity = {0: 0}

    for i, s in enumerate(S):
        parity ^= 2**s
        ans = i+1
        if parity in dict_parity:
            ans = min(ans, dict_parity[parity]+1)
        ans = min(
            [ans]+[dict_parity.get(parity ^ 2**j, ans)+1 for j in range(26)])
        dict_parity[parity] = min(ans, dict_parity.get(parity, ans))
    print(ans)


main()
