# include <bits/stdc++.h>

using namespace std ;

typedef long double ld ;
const ld PI = acos(-1) ;

int main(){
    int h , r , da , dw ; cin >> h >> r >> da >> dw ;
    auto f = [&]( ld mid ){
        ld w = PI * mid * r * r * dw ;
        ld a = PI * ( h - mid ) * r * r * da ;
        return ( w * h/2 + a * ( mid + (h - mid)/2 )  )/( w + a ) ;
    };
    ld s = 0 , e = h ;
    for (int i = 0; i < 100; ++i) {
        ld m1 = s + 1.0*(e-s)/3 ;
        ld m2 = e - 1.0*(e-s)/3 ;
        if ( f(m1) <= f(m2) ){
            s = m1 ;
        }else{
            e = m2 ;
        }
    }
    cout << fixed << setprecision(10) << s ;
    return 0 ;
}