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

int main() {
  double a, b, x, y;
  cin >> a >> b >> x >> y;
  double res;
  if (x * b >= y * a) {
    res = y + (a / b) * y;
  } else {
    res = x + (b / a) * x;
  }
  printf("%.5f", res);
}