import java.util.*;
import java.lang.*;
import java.io.*;
 
 
class Calculator {
    int left, right;
 
    public Calculator(){}
 
    public Calculator(int left, int right){
        this.left = left;
        this.right = right;
    }
 
 
 
    public void sum() {
        System.out.println(this.left + this.right);
    }
 
    public void avg() {
        System.out.println((this.left + this.right) / 2);
    }
}
class SubstractionableCalculator extends Calculator {
    public SubstractionableCalculator(int left, int right) {
        super(left, right);
    }
 
    public void substract() {
        System.out.println(this.left - this.right);
    }
}
 
class CalculatorConstructorDemo5 {
    public static void main(String[] args) {
 
        Calculator c1 = new Calculator(10, 20);
        c1.sum();
        c1.avg();
 
        SubstractionableCalculator c2 = new SubstractionableCalculator();
          c2.substract();
    }
}

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