#include using namespace std; #define int long long using ll=long long; using vi=vector; using vl=vector; using pii=pair; using pll=pair; #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 ostream& operator << (ostream &os, const vector &v) { ITR(i,v) os<<*i<<(i==end(v)-1?"":" "); return os; } template istream& operator >> (istream &is, vector &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 ans=0; while(d>EPS) { double t=d/(w+vr); ans+=w*t; d-=(vl+vr)*t; swap(vl,vr); } printf("%.10f\n",ans); return 0; }