#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <stack>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

int main(){
  double vl, vr, d, w;

  cin >> vl >> vr;
  cin >> d;
  cin >> w;

  double ret = 0;
  int turn = 0;
  vector<double> v;
  rep(i,10){
    double t;
    if(turn == 0){
      t = d/(w+vr);
    }else{
      t = d/(w+vl);
    }

    v.push_back(w*t);
    ret += w * t;
    d -= vr * t + vl * t;
    turn = 1 - turn;
  }

  double a = v[0] + v[1];
  double r = (v[2] + v[3]) / (v[0] + v[1]);
  ret = a / (1-r);
  
  printf("%.12lf\n", ret);
  
  return 0;
}