output_description: Print the minimum number of stones that needs to be recolored.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      S
attempt: inp_num = int(input())
  inp = input()
  w1 = 0
  b1 = 0
  
  bf = 0
  wf = 0
  
  for i in range(len(inp)):
      if inp[i] == "#" and wf == 0:
          wf = 1
          b1 = b1 + 1
      elif inp[i] == "#" and wf == 1:
          b1 = b1 + 1
      elif inp[i] == "." and wf == 1:
          w1 = w1 + 1
  
  w2 = 0
  b2 = 0
  
  for i in range(len(inp)):
      if inp[len(inp) - i - 1] == "." and bf == 0:
          bf = 1
          w2 = w2 + 1
      elif inp[len(inp) - i - 1] == "#" and bf == 1:
          b2 = b2 + 1
      elif inp[len(inp) - i - 1] == "." and bf == 1:
          w2 = w2 + 1
  
  line = [b1, w1, b2, w2]
  # print(line)
  print(min(line))
  
problem_description: Statement
  
  There are N stones arranged in a row. Every stone is painted white or black. A
  string S represents the color of the stones. The i-th stone from the left is
  white if the i-th character of S is `.`, and the stone is black if the
  character is `#`.
  
  Takahashi wants to change the colors of some stones to black or white so that
  there will be no white stone immediately to the right of a black stone. Find
  the minimum number of stones that needs to be recolored.
samples: [{"input": "3\n    #.#", "output": "1\n    \n\nIt is enough to change the color of the first stone to white.\n\n* * *"}, {"input": "5\n    #.##.", "output": "2\n    \n\n* * *"}, {"input": "9\n    .........", "output": "0"}]