output_description: If a+b=15, print `+`; if a\times b=15, print `*`; if neither holds, print `x`.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      a b
attempt: n,m,d = map(int,input().split())
  
  """
  #kuso code
  start = time.time()
  a = [random.randrange(n) for i in range(m)]
  a = np.array(a)
  b = np.abs(a[1:]-a[:-1])
  cnt = np.sum(b == d)
  ave = cnt
  
  i = 0
  while(time.time() - start < 10):
      a = [random.randrange(n) for i in range(m)]
      a = np.array(a)
      b = np.abs(a[1:]-a[:-1])
      cnt = np.sum(b == d)
      ave = ((i+1)*ave + cnt)/(i+2)
      i += 1
  print(ave)
  """
  
  oks*n = 2*np.max(n-2*d,0) + 2*d)
  ave = oks*(m-1)/n/n
  print(ave)
problem_description: Statement
  
  You are given two integers a and b. Determine if a+b=15 or a\times b=15 or
  neither holds.
  
  Note that a+b=15 and a\times b=15 do not hold at the same time.
samples: [{"input": "4 11", "output": "+\n    \n\n4+11=15.\n\n* * *"}, {"input": "3 5", "output": "*\n    \n\n3\\times 5=15.\n\n* * *"}, {"input": "1 1", "output": "x\n    \n\n1+1=2 and 1\\times 1=1, neither of which is 15."}]