#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <functional>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cctype>
#include <string>

using namespace std;

int main() {
  double a, b, x, y;
  cin >> a >> b >> x >> y;
  if (x*b/a <= y) {
    printf("%.20lf\n", x*b/a+x);
  }else {
    printf("%.20lf\n", y*a/b+y);
  }
}