import java.util.*;

class mymath {
	long a;
	long b;

	long add() {
		System.out.print("instance");
		return a + b;
	}

	long sub() {
		System.out.println("instance");
		return a - b;
	}

	long mul() {
		System.out.println("instance");
		return a * b;
	}

	long div() {
		System.out.println("instance");
		return a / b;
	} // 그냥 메소드

	static long add(long a, long b) {
		return a + b;
	}

	static long sub(long a, long b) {
		return a - b;
	}

	static long mul(long a, long b) {
		return a * b;
	}

	static long div(long a, long b) {
		return a / b;
	}
}

public class static_method {
	public static void main(String[] args) {
		System.out.println(mymath.add(20L, 30L));
		mymath start = new mymath();
		start.a = 100L;
		start.b = 200L;
		System.out.println(start.add());
	}

}

}