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(i) for i in input().split())
  
  # H, W, A, B = (2, 3, 1, 1)
  
  # 初期化
  # W行 H列
  mat = [[0 for x in range(W)] for y in range(H)]
  
  # AかつBに−１を代入
  for y in range(H - A, H):
      for x in range(0, B):
          mat[y][x] = -1
  
  # 歩ける数を代入
  for y in range(H):
      for x in range(W):
          # 右端でも左端でもない
          if (x != W - 1) and (y != H - 1):
              # 右が空
              if mat[y][x + 1] == 0:
                  mat[y][x] += 1
              # 下が空
              if mat[y + 1][x] == 0:
                  mat[y][x] += 1
          # 右端のみ
          elif (x == W - 1) and (y != H - 1):
              # 下が空
              if mat[y + 1][x] == 0:
                  mat[y][x] += 1
          # 下端のみ
          elif (x != W - 1) and (y == H - 1):
              # 右が空
              if mat[y][x + 1] == 0:
                  mat[y][x] += 1
  
  # ゴールまでのパターン数を計算
  cnt = 0
  for y in range(H):
      for x in range(W):
          if mat[y][x] == 2:
              cnt += 1
  pattern_num = 2**cnt
  print(pattern_num)
  
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"}]