#include <bits/stdc++.h>

typedef long double ld;
typedef long long ll;
using namespace std;
int di[] = {1, 0, -1, 0, 0, 1, -1, 1};
int dj[] = {0, 1, 0, -1, -1, 0, 1, -1};
const ll oo = 1e18, MOD = 1e9 + 7;
const int N = 1e6 + 5, M = 30005;
#define EPS 1e-9

int t, n, m, ans;
int dp[N];
vector<int> g[N];
/*void solve(){

}
void dfs(int s,int p,int lvl){
    dp[s] = {lvl,lvl};
    for(auto it:g[s]){
        if(it != p){
            dfs(it, s, lvl + 1);
        }
    }
}*/
int main() {
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    //freopen("output.txt", "w", stdout);
    /*cin >> n;
    for(int i = 1; i < n ;++i){
        int u,v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }*/
    ld h,r,da,dw;
    cin>>h>>r>>da>>dw;
    ld lo=0,hi=h;
    ld ans;
    while(hi-lo>EPS)
    {
        ld mid1=lo+(hi-lo)/3.0,mid2=hi-(hi-lo)/3.0;
        ld tmp1=((h-mid1)*0.5+mid1-mid1*0.5)*da*(h-mid1)/(dw*mid1+da*(h-mid1))+mid1*0.5;
        ld tmp2=((h-mid2)*0.5+mid2-mid2*0.5)*da*(h-mid2)/(dw*mid2+da*(h-mid2))+mid2*0.5;
        if(tmp1<tmp2)
        {
            ans=mid1;
            hi=mid2;

        }
        else lo=mid1;

    }
    cout<<fixed<<setprecision(10)<<lo;
    return 0;
}