import strutils, sequtils

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

var
  (Aw, Ab) = (Awb[0], Awb[1])
  (Bw, Bb) = (Bwb[0], Bwb[1])
  
  Cw = max(0, C - Ab)

Aw -= Cw
Bw += Cw

Aw += min(D, Bw)

echo Aw