#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll=long long;
using vi=vector<int>;
using vl=vector<long long>;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
#define ITR(v,c) for(auto v=begin(c);v!=end(c);++v)
#define FORE(x,c) for(auto &x:c)
#define FOR(v,a,n) for(int v=a;v<(int)(n);++v)
#define REP(v,n) FOR(v,0,n)
#define RREP(v,n) for(int v=((int)(n)-1);v>=0;--v)
#define ALL(c) begin(c),end(c)
#define RALL(c) rbegin(c),rend(c)
#define SZ(c) ((int)c.size())
#define dump(...)
const int DX[9]={0,1,0,-1,1,1,-1,-1,0}, DY[9]={-1,0,1,0,-1,1,1,-1,0};
const int INF=1e9*2; const long long INFLL=1e18*2;
template<class T> ostream& operator << (ostream &os, const vector<T> &v) {
    ITR(i,v) os<<*i<<(i==end(v)-1?"":" "); return os; }
template<class T> istream& operator >> (istream &is, vector<T> &v) {
    ITR(i,v) is>>*i; return is; }
//------------------------------------------------------------------------------

const double EPS=1e-7;
signed main() {
    double vl,vr,d,w;
    cin>>vl>>vr>>d>>w;
    double a,r=1;
    {
        double t=d/(w+vr);
        a=w*t;
        d-=(vl+vr)*t;
        swap(vl,vr);
        double b=a;

        t=d/(w+vr);
        r=(w*t)/b;
        swap(vl,vr);

        t=d/(w+vr);
        r=(w*t)/b;
        swap(vl,vr);
    }

    printf("%.7f\n",a/(1-r));
    return 0;
}