#include <bits/stdc++.h>

using namespace std;

int main() {
    double a, b, x, y;
    cin >> a >> b >> x >> y;
    double ans;
    if (y >= x * b / a) {
        ans = x + x * b / a;
    } else {
        ans = y + y * a / b;
    }

    cout << fixed << setprecision(7);
    cout << ans << endl;
    return 0;
}