public static Integer add(Integer a, Integer b) {
		if (a > 0 && b > 0 && a + b < 0) {
			throw new ArithmeticException("integer overflow");
		} else if (a < 0 && b < 0 && a + b > 0) {
			throw new ArithmeticException("integer underflow");
		} else {return a + b;}
		
	}