#include <bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define mp(a,b) make_pair(a,b)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;

#define INF INT_MAX/3

#define MAX_N 1000
#define EPS 1e-7

double v1,v2,d,w;

int main(){
	cin.sync_with_stdio(false);
	cin>>v1>>v2>>d>>w;
	double res=0;
	double a=(w/(w+v2))*d+(w/(w+v1))*((w-v1)/(w+v2))*d;
	double r=((w-v2)/(w+v1))*((w-v1)/(w+v2));
	printf("%.10f\n", a/(1-r));
	return 0;
}