import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time,copy,functools

sys.setrecursionlimit(10**7)
inf = 10**20
eps = 1.0 / 10**15
mod = 10**9+7

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LI_(): return [int(x)-1 for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def LS(): return sys.stdin.readline().split()
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def S(): return input()
def pf(s): return print(s, flush=True)


def main():
    a = [2**(ord(c)-97) for c in S()]
    b = [0]
    d = {}
    d[0] = 0
    c = 0
    ii = [2**i for i in range(26)]
    for t,i in zip(a, range(1,len(a)+1)):
        c ^= t
        tr = inf
        if c in d:
            tr = b[d[c]] + 1
        else:
            d[c] = i

        for j in ii:
            e = c ^ j
            if e in d and b[d[e]] + 1 < tr:
                tr = b[d[e]] + 1
        b.append(tr)
    return b[-1]



print(main())


