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

int main(){
	int a,b,x,y; cin>>a>>b>>x>>y;
	if(a==b) cout<< min(x,y)*2 <<endl;
	else if(a>b) cout<<fixed<<setprecision(12)<< x+(double)x*a/b <<endl;
	else cout<<fixed<<setprecision(12)<< y+(double)y*a/b <<endl;
}