output_description: Print the average of the beauties of the sequences of length m where each
  element is an integer between 1 and n. The output will be judged correct if
  the absolute or relative error is at most 10^{-6}.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      n m d
attempt: def main():
    	t = input().split(" ")
      n, m, d = int(t[0]), int(t[1]), int(t[2])
      if d == 0:
      	r = (m-1) / n
      elif d > n:
        	r = 0
      else:
        	r = 2 * (n-d) * (m-1) / n / n
      print(r)
  main()
problem_description: Statement
  
  Let us define the _beauty_ of a sequence (a_1,... ,a_n) as the number of pairs
  of two adjacent elements in it whose absolute differences are d. For example,
  when d=1, the beauty of the sequence (3, 2, 3, 10, 9) is 3.
  
  There are a total of n^m sequences of length m where each element is an
  integer between 1 and n (inclusive). Find the beauty of each of these n^m
  sequences, and print the average of those values.
samples: [{"input": "2 3 1", "output": "1.0000000000\n    \n\nThe beauty of (1,1,1) is 0.  \nThe beauty of (1,1,2) is 1.  \nThe beauty of (1,2,1) is 2.  \nThe beauty of (1,2,2) is 1.  \nThe beauty of (2,1,1) is 1.  \nThe beauty of (2,1,2) is 2.  \nThe beauty of (2,2,1) is 1.  \nThe beauty of (2,2,2) is 0.  \nThe answer is the average of these values: (0+1+2+1+1+2+1+0)/8=1.\n\n* * *"}, {"input": "1000000000 180707 0", "output": "0.0001807060"}]