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

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