output_description: Print the largest possible number of different letters contained in both X and
  Y.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      S
attempt: N = int(input())
  text = input()
  result = []
  for i in range(N - 2):
      counter = 0
      text1 = text[0 : i + 2]
      text2 = text[i + 2 :]
      if "a" in text1 and text2:
          counter = counter + 1
      if "b" in text1 and text2:
          counter = counter + 1
      if "c" in text1 and text2:
          counter = counter + 1
      if "d" in text1 and text2:
          counter = counter + 1
      if "e" in text1 and text2:
          counter = counter + 1
      if "f" in text1 and text2:
          counter = counter + 1
      if "g" in text1 and text2:
          counter = counter + 1
      if "h" in text1 and text2:
          counter = counter + 1
      if "i" in text1 and text2:
          counter = counter + 1
      if "j" in text1 and text2:
          counter = counter + 1
      if "k" in text1 and text2:
          counter = counter + 1
      if "l" in text1 and text2:
          counter = counter + 1
      if "m" in text1 and text2:
          counter = counter + 1
      if "n" in text1 and text2:
          counter = counter + 1
      if "o" in text1 and text2:
          counter = counter + 1
      if "p" in text1 and text2:
          counter = counter + 1
      if "q" in text1 and text2:
          counter = counter + 1
      if "r" in text1 and text2:
          counter = counter + 1
      if "s" in text1 and text2:
          counter = counter + 1
      if "t" in text1 and text2:
          counter = counter + 1
      if "u" in text1 and text2:
          counter = counter + 1
      if "v" in text1 and text2:
          counter = counter + 1
      if "w" in text1 and text2:
          counter = counter + 1
      if "x" in text1 and text2:
          counter = counter + 1
      if "y" in text1 and text2:
          counter = counter + 1
      if "z" in text1 and text2:
          counter = counter + 1
      result = result + [counter]
  
  print(max(result))
  
problem_description: Statement
  
  You are given a string S of length N consisting of lowercase English letters.
  We will cut this string at one position into two strings X and Y. Here, we
  would like to maximize the number of different letters contained in both X and
  Y. Find the largest possible number of different letters contained in both X
  and Y when we cut the string at the optimal position.
samples: [{"input": "6\n    aabbca", "output": "2\n    \n\nIf we cut the string between the third and fourth letters into X = `aab` and Y\n= `bca`, the letters contained in both X and Y are `a` and `b`. There will\nnever be three or more different letters contained in both X and Y, so the\nanswer is 2.\n\n* * *"}, {"input": "10\n    aaaaaaaaaa", "output": "1\n    \n\nHowever we divide S, only `a` will be contained in both X and Y.\n\n* * *"}, {"input": "45\n    tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir", "output": "9"}]