import strutils, sequtils

let
  Awb, Bwb, CD = stdin.readLine.split.map parseInt
  (C, D) = (CD[0], CD[1])

var
  white = (numA: Awb[0], numB: Bwb[0])
  black = (numA: Awb[1], numB: Bwb[1])

  num = max(0, C - black.numA)

white.numA -= num
white.numB += num

white.numA += min(D, white.numB)

echo white.numA