text: try:
      while True:
          string = str(input())
          string = string.lower()
          counter = [0] * 26
          for i in range(len(string)):
              if 'a' <= string[i] and string[i] <= 'z':
                  counter[ord(string[i]) - ord('a')] += 1
          oddCounter = 0
          for count in counter:
              if count % 2 == 1:
                  oddCounter += 1
          print("no...") if oddCounter > 1 else print("yes !")
  except EOFError:
      pass