#include <bits/stdc++.h>

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<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> 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<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-15;

int main() {
	long double vl, vr, d, w;
	cin >> vl >> vr >> d >> w;
	
	long double t = 0.0;
	
	while (true) {
		long double nd = d - (vl * t + vr * t);
		
		long double nt = nd / (w + vr);
		
		t += nt;
		
		if (nt <= EPS) break;
		
		swap(vr, vl);
	}
	
	printf("%.15Lf\n", t * w);
	
	return 0;
}