import java.util.*;
import java.lang.*;
import java.io.*;

// The main method must be in a class named "Main".
interface Parent{
    void run();
}

interface Child{
    int sum(int a,int b);
}
class Main {
    public static void main(String[] args) {
        Parent p=()->System.out.println("running");
        p.run();
        Child c=(a,b)-> a+b;
        System.out.println(c.sum(10,20));
        Child d=(a,b)->{
            int relsum=a+b;
            if(relsum>0){
                return relsum;
            }
            return 0;
    };
        System.out.println(d.sum(10,20)); 
   }
}