import times, strutils, sequtils, math, algorithm, tables, sets, lists, intsets import critbits, future, strformat, deques template `max=`(x,y) = x = max(x,y) template `min=`(x,y) = x = min(x,y) template `mod=`(x,y) = x = x mod y template scan2 = (scan(), scan()) template scan3 = (scan(), scan()) let read* = iterator: string {.closure.} = while true: (for s in stdin.readLine.split: yield s) proc scan(): int = read().parseInt proc scanf(): float = read().parseFloat proc toInt(c:char): int = return int(c) - int('0') var D = 1E9.int+7 m:int = 1E6.int fac:seq[int] finv:seq[int] inv:seq[int] proc comInit()= fac = newseqwith(m,1) finv = newseqwith(m,1) inv = newseqwith(m,1) for i in 2..0: if (n and 1)>0: result*=x result.mod=md n = n shr 1 x = x*x x.mod=md proc solve():int= var md = 10^9+7 (a,b)=(scan().mod(md),scan().mod(md)) (n,k)=(scan(),scan()) sm = 0 ca = com(n-1,k-1) cb = com(n-1,k-2) echo (ca*a+cb*b).mod(md) for i in 0..n+1: sm += ((com(n-1,i-1)*a+com(n-1,i-2)*b).mod(md))^2 sm.mod=md return sm echo solve()