#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<vector>
#include<map>
#include<queue>
#include<string>
#include<sstream>
#include<cmath>
using namespace std;

int main(){

  double a, b, x, y;
  cin >> a >> b >> x >> y;

  if( a*y < b*x ) printf("%.8lf\n", y + y * a / b);
  else printf("%.8lf\n", x + x * b / a);

  return 0;
}