def main():
    # print(*answers, sep=os.linesep)
    from collections import Counter
    
    c = Counter(input())
    
    s = sum(c.values())
    n = len(list(filter(lambda v: v % 2 == 1, c.values())))
    
    if n == 0:
      print(s)
    else:
      t = ((s-n) /2)//n
    
      print(int(1+t*2))

    
main()