#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MOD 1000000007
#define INF (1LL<<25)     //33554432
#define PI 3.14159265359
#define EPS 1e-12
//#define int ll

signed main(void)
{
  int vl, vr, d, w;
  cin >> vl >> vr >> d >> w;

  double ret = 0, l = 0, r = d;
  bool to_right = true;
  REP(i, 1000000) {
    if(to_right) {
      double t = (r-l)/(w+vr);
      l +=  vl*t;
      r -= vr*t;
      ret += w*t;
    } else {
      double t = (r-l)/(w+vl);
      l += vl*t;
      r -= vr*t;
      ret += w*t;
    }
    to_right = !to_right;
  }

  cout << fixed << setprecision(15) << ret << endl;

  return 0;
}