/* -*- coding: utf-8 -*-
 *
 * 236.cc: No.236 鴛鴦茶 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  double a, b, x, y;
  cin >> a >> b >> x >> y;

  double x0 = y * a / b;
  double y0 = x * b / a;

  double ans = (x < x0) ? x + y0 : x0 + y;
  printf("%.8lf\n", ans);

  return 0;
}