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: import math
  from itertools import combinations
  from collections import Counter
  
  
  def solve(H, W, A, B):
      ans = 0
      R = 10**9 + 7
  
      p1_y = math.factorial(H - 1 - A)
      d2_y = math.factorial(H - 1 - (H - A))
      way1 = -1
      way3 = -1
  
      for i in range(0, W - B):
          p1 = (B + i, H - 1 - A)
          p2 = (B + i, H - A)
          e = (W - 1, H - 1)
          d2 = (e[0] - p2[0], e[1] - p2[1])
  
          if way1 == -1:
              way1 = math.factorial(p1[0] + p1[1]) // math.factorial(p1[0]) // p1_y
          else:
              way1 *= p1[0] + p1[1]
              way1 //= p1[0]
  
          if way3 == -1:
              way3 = math.factorial(d2[0] + d2[1]) // math.factorial(d2[0]) // d2_y
          else:
              way3 *= d2[0] + 1
              way3 //= d2[0] + d2[1] + 1
          ans += way1 * way3
          way1 %= R
          way3 %= R
      return ans % R
  
  
  if __name__ == "__main__":
      H, W, A, B = map(int, input().split(" "))
      print(solve(H, W, A, B))
  
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"}]