#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

int main(){
  int A, B, X, Y; cin >> A >> B >> X >> Y;
  double ans = 0.0;
  if(A*Y >= B*X){
    ans = (double)X + (double)X*B/A;
  }else{
    ans = (double)Y + (double)Y*A/B;
  }
  cout << setprecision(10) << ans << endl;
}