interface W {
    void sum();
}

interface S extends W {
    void sub();
}

class K implements S {
    @Override
    public void sum() {
        int a = 10, b = 20, sum;
        sum = a + b;
        System.out.println(sum);
    }

    @Override
    public void sub() {
        int a = 20, b = 10, sub;
        sub = a - b; // Fix: Corrected the subtraction operation
        System.out.println(sub);
    }
}

class D {
    public static void main(String[] args) {
        K r = new K();
        r.sum();
        r.sub(); // Fix: Corrected the method call
    }
}