#include <iostream>
#include <math.h>
#include <vector>
#include <iomanip>
using namespace std;
#define P(x) cout << x << endl
#define rep(i,n) for(int i=0;i<n;i++)
int main(){
    double a,b,x,y,ans;
    cin>>a>>b>>x>>y;
    if(x*b/a <= y){
        ans = x * (a+b)/a;
    }else{
        ans = y * (a+b)/b;
    }
   std::cout << std::setprecision(100) << ans; 
}