import java.io.*;
import java.text.*;
class test{
public static void main(String[]x)throws Exception{
BufferedReader i=new BufferedReader(new InputStreamReader(System.in));
for(String s=i.readLine();s!=null;s=i.readLine()){
String[] t=s.split(" ");
float a=Float.valueOf(t[0]);
float b=Float.valueOf(t[1]);
System.out.println(new DecimalFormat("0.00").format(a*b/(a+b)));
}
}
}