output_description: Print the minimum number of operations required.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      A
      B
      C
attempt: n = int(input())
  a = input()
  b = input()
  c = input()
  cnt2 = 0
  cnt3 = 0
  for i in range(n):
    nsame = len(set([a[i], b[i], c[i]]))
      if nsame == 2:
        cnt2 += 1
      elif nsame == 1:
        cnt3 += 1
  ans = 2*n - cnt2 - 2*cnt3
  print(ans)
      
problem_description: Statement
  
  You are given three strings A, B and C. Each of these is a string of length N
  consisting of lowercase English letters.
  
  Our objective is to make all these three strings equal. For that, you can
  repeatedly perform the following operation:
  
    * Operation: Choose one of the strings A, B and C, and specify an integer i between 1 and N (inclusive). Change the i-th character from the beginning of the chosen string to some other lowercase English letter.
  
  What is the minimum number of operations required to achieve the objective?
samples: [{"input": "4\n    west\n    east\n    wait", "output": "3\n    \n\nIn this sample, initially A = `west`\u3001B = `east`\u3001C = `wait`. We can achieve the\nobjective in the minimum number of operations by performing three operations\nas follows:\n\n  * Change the second character in A to `a`. A is now `wast`.\n  * Change the first character in B to `w`. B is now `wast`.\n  * Change the third character in C to `s`. C is now `wast`.\n\n* * *"}, {"input": "9\n    different\n    different\n    different", "output": "0\n    \n\nIf A, B and C are already equal in the beginning, the number of operations\nrequired is 0.\n\n* * *"}, {"input": "7\n    zenkoku\n    touitsu\n    program", "output": "13"}]