#include <iostream>
#include <vector>
#include <tuple>
#include <algorithm>
#include <iomanip>
using namespace std;
using ll = long long;

int main() {
    int a, b;
    double x, y;
    cin >> a >> b >> x >> y;
    cout << fixed << setprecision(10);
    if(x >= y * a / b) {
        cout << y + y * a / b << endl;
    } else {
        cout << x + x * b / a << endl;
    }
}