#include <bits/stdc++.h>
using namespace std;

using ld=long double;

signed main(){
  ld a,b,x,y;cin>>a>>b>>x>>y;
  ld ans=0;
  if(y*a>=x*b)ans=(a+b)*x/a;
  else ans=(a+b)*y/b;
  cout<<fixed<<setprecision(12)<<ans<<endl;
}