output_description: Print the number of ways she can travel to the bottom-right cell, modulo
  10^9+7.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      H W A B
attempt: H, W, A, B = [int(n) for n in input().split(" ")]
  answers = []
  for total in range(B, W):
      disp = 1
      for n in range(1, total + (H - A)):
          disp *= n
      for m in range(1, H - A):
          disp //= m
      for t in range(1, total + 1):
          disp //= t
      answers.append(disp)
  for cnt, total in enumerate(range(B, W)):
      disp = 1
      for n in range(1, (W - total - 1) + (H - (H - A))):
          disp *= n
      for m in range(1, H - (H - A)):
          disp //= m
      for t in range(1, W - total):
          disp //= t
      answers[cnt] *= disp
  print(sum(answers))
  
problem_description: Statement
  
  We have a large square grid with H rows and W columns. Iroha is now standing
  in the top-left cell. She will repeat going right or down to the adjacent
  cell, until she reaches the bottom-right cell.
  
  However, she cannot enter the cells in the intersection of the bottom A rows
  and the leftmost B columns. (That is, there are A×B forbidden cells.) There is
  no restriction on entering the other cells.
  
  Find the number of ways she can travel to the bottom-right cell.
  
  Since this number can be extremely large, print the number modulo 10^9+7.
samples: [{"input": "2 3 1 1", "output": "2\n    \n\nWe have a 2\u00d73 grid, but entering the bottom-left cell is forbidden. The number\nof ways to travel is two: \"Right, Right, Down\" and \"Right, Down, Right\".\n\n* * *"}, {"input": "10 7 3 4", "output": "3570\n    \n\nThere are 12 forbidden cells.\n\n* * *"}, {"input": "100000 100000 99999 99999", "output": "1\n    \n\n* * *"}, {"input": "100000 100000 44444 55555", "output": "738162020"}]