#include <bits/stdc++.h>

using namespace std;

const double PI = acos(-1);

int main(){
    double d, s, r, o;
    cin >> d >> s >> r >> o;

    bool tl = false, ts = false, jr = false;
    double mx = -10.0;

    for(double i = 0.0; i <= 2.0*r; i += 0.01)
        mx = max(mx, 2.0*i*acos(i/(2.0*r)) - PI*i*d/s);
    
    if(mx - o < -0.05){
        cout << "-2.0\n";
        return 0;
    }else if(mx - o <= 0.05){
        cout << "0.0\n";
        return 0;
    }

    for(double i = 0.01; i <= s - 2.0*r; i += 0.01){
        tl = false, ts = false, jr = false;
        mx = -10.0;

        for(double j = 0; j <= 2.0*r; j += 0.01)
            mx = max(mx, 2.0*(j+i)*acos(((i+j)*(i+j) - r*r + (r+i)*(r+i))/(2*(r+i)*(i+j))) - PI*(j+i)*d/s);
        
        if(mx - o < 0.05 && mx - o > -0.05){
            cout << setprecision(1) << fixed << (s - i - 2.0*r) << "\n";
            return 0;
        }
    }
    
    cout << "-1.0\n";
    return 0;
}