#include <iostream>
#include <iomanip>
using namespace std;

int main(){
  double a,b,x,y,z,r;
  cin>>a>>b>>x>>y;
  double f1,f2;
  f1=a*y;
  f2=b*x;
  if(f1<f2){
    r=f1/f2;
    x*=r;
    z=x+y;
  } else if(f1>f2){
    r=f2/f1;
    y*=r;
    z=x+y;
  } else {
    z=x+y;
  }
  cout<<fixed<<setprecision(9)<<z<<endl;
  return 0;
}