import std.stdio;
import std.array;
import std.string;
import std.conv;
import std.algorithm;
import std.typecons;
import std.range;
import std.random;
import std.math;
import std.container;
import std.numeric;
import std.bigint;


void main() {
  auto input = readln.split.map!(to!real);
  auto vl = input[0];
  auto vr = input[1];
  auto d1 = readln.chomp.to!real;
  auto w = readln.chomp.to!real;

  real EPS = 0.00000001;
  real a = 0.0;
  real t1, t2, a1, a2, d2;
  foreach (i; 0..10^^7) {
    t1 = d1 / (vl + w);
    a1 = w * t1;
    if (a1 < EPS)
      break;
    a += a1;
    d2 = d1-(vl+vr)*t1;
    t2 = d2 / (vl+w);
    a2 = w * t2;
    if (a2 < EPS)
      break;
    a += a2;
    d1 = d2-(vl+vr)*t2;
  }
  writefln("%.7f", a);
}