#include <bits/stdc++.h>
using namespace std;
int main() {
    // Input
    int A, B, X, Y;
    cin >> A >> B >> X >> Y;

    // Output
    cout << fixed << setprecision(20);
    if (B * X <= A * Y) {
        double wolongcha = (double) X * (A + B) / A;
        cout << wolongcha << endl;
    } else {
        double wolongcha = (double) Y * (A + B) / B;
        cout << wolongcha << endl;
    }
}