#include <cstdio>
#include <algorithm>
#include <iostream>
#include <vector>
#define wr (w+vr)
#define wl (w+vl)
using namespace std;

int main(void){

  double vl,vr,d,w;
  double res=0.0,t;
  scanf("%lf %lf %lf %lf",&vl,&vr,&d,&w);
  bool r=true;
  while(d>0.000001){
    if(r) t=d/wr;
    else t=d/wl;
    res+=w*t;
    d-=(vr+vl)*t;
  }
  printf("%.10f\n",res);
  return 0;
}