#include <iostream>
#include <iomanip>
using namespace std;

int main() {
  double a, b, x, y, ans;
  cin >> a >> b >> x >> y;
  if (x * b / a <= y) ans = x + x * b / a;
  else ans = y + y * a / b;
  cout << fixed << setprecision(8) << ans << endl;
}