import Data.Array.IArray
main = do
    [h,w,a,b] <- return . map (read::String->Int) . words =<< getLine
    let	basicArray::Array (Int,Int) (Int,Int)
	basicArray = listArray ((1,1),(h,w))
			[(ro,co) | ro<-[1..h], co<-[1..w]]
	memz = 
	  let
	    zenka (r,c)	| r<=h-a    = ((fact $ c-1+r-1) `div` fact (c-1)) `div` fact (r-1)
			| c==b+1    = memz (r-1,c)
			| otherwise = memz (r,c-1) + memz (r-1,c)
	      where
		fact::Int->Integer
		fact 0 = 1
		fact n = toInteger n*fact (n-1)
	    zarray = amap zenka basicArray
	  in (zarray!)
    print $ memz (h,w) `mod` (10^9 + 7)
