#include using namespace std; #define FOR(i,a,b) for(int i=(a);i<(b);i++) #define REP(i,n) FOR(i,0,n) #define ALL(v) (v).begin(),(v).end() template inline bool chmax(A &a, B b) { if (a inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; } typedef unsigned long long ull; typedef long long ll; typedef pair pii; typedef pair pll; typedef pair P; const ll INF = 1ll<<29; const ll MOD = 1000000007; const double EPS = 1e-8; int main() { long double vl, vr, d, w; cin >> vl >> vr >> d >> w; long double t = 0.0; REP(i, 10000) { long double nd = d - (vl * t + vr * t); long double nt = nd / (w + vr); t += nt; swap(vr, vl); } printf("%.15Lf\n", t * w); return 0; }