output_description: Print the length of the shortest string that satisfies the conditions.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      N
      s
      t
attempt: N, S, T = (input() for i in range(3))
  N = int(N)
  for k in range(N, -1, -1):  # k文字共通
      if all([S[N - k + i] == T[i] for i in range(k)]) or k == 0:
          print(S + T[k:])
          break
  
problem_description: Statement
  
  Snuke is interested in strings that satisfy the following conditions:
  
    * The length of the string is at least N.
    * The first N characters equal to the string s.
    * The last N characters equal to the string t.
  
  Find the length of the shortest string that satisfies the conditions.
samples: [{"input": "3\n    abc\n    cde", "output": "5\n    \n\nThe shortest string is `abcde`.\n\n* * *"}, {"input": "1\n    a\n    z", "output": "2\n    \n\nThe shortest string is `az`.\n\n* * *"}, {"input": "4\n    expr\n    expr", "output": "4\n    \n\nThe shortest string is `expr`."}]