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


int main() {
    double A, B, X, Y; cin >> A >> B >> X >> Y;
    if(A==B) cout << min(X, Y)*2 << endl;
    else if(A<B){
        if(Y*A/B<X) cout << fixed<< Y+Y*A/B << endl;
        else cout <<fixed<< X*B/A+X << endl; 
    }else if(A>B){
        if(X*B/A<Y) cout <<fixed << X+X*B/A << endl;
        else cout << fixed <<Y*A/B+Y << endl; 
    }
    return 0;
}