import strutils, sequtils

let
  tmp = stdin.readline.split.map(parseInt)
  (vl, vr) = (tmp[0], tmp[1])
var d = stdin.readline.parseFloat
let w = stdin.readline.parseInt

var ans = 0.0

#while d.abs > 1e-7:
for _ in 0..10000:
  let
    t1 = d / (vr + w).float
    t2 = (d - (vl + vr).float * t1) / (vl + w).float
  ans += (t1 + t2) * w.float
  # echo((t1 + t2) * w.float)
  d -= (t1 + t2) * (vl + vr).float
ans.echo