output_description: Print the number of the subsequences such that all characters are different,
  modulo 10^9+7.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      S
attempt: A = int(input())
  V = list(input())
  v = len(list(set(V)))
  a = 0
  if A - v == 0:
      a = 1
  else:
      a = A - v
  q = ((2**v) - 1) * a
  print(q)
  
problem_description: Statement
  
  You are given a string S of length N. Among its subsequences, count the ones
  such that all characters are different, modulo 10^9+7. Two subsequences are
  considered different if their characters come from different positions in the
  string, even if they are the same as strings.
  
  Here, a subsequence of a string is a concatenation of **one or more**
  characters from the string without changing the order.
samples: [{"input": "4\n    abcd", "output": "15\n    \n\nSince all characters in S itself are different, all its subsequences satisfy\nthe condition.\n\n* * *"}, {"input": "3\n    baa", "output": "5\n    \n\nThe answer is five: `b`, two occurrences of `a`, two occurrences of `ba`. Note\nthat we do not count `baa`, since it contains two `a`s.\n\n* * *"}, {"input": "5\n    abcab", "output": "17"}]