#include<iostream>
#include<string>
#include<algorithm>
#include<cmath>
#include<iomanip>
#include<cstring>
#include<map>
#include<vector>
#include<queue>
using namespace std;
typedef long long int ll;

int main(){

  double a, b, x, y;
  cin >> a >> b >> x >> y;
  if(b*x/a>y){
    cout << setprecision(10) << a*y/b+y << endl;
  } else {
    cout << setprecision(10) << b*x/a+x << endl;
  }
  
  return 0;
}