public int addNum(int numA, int numB){
		System.out.println("A: " + numA + ", B: " + numB);		
		if(numA > 15 || numB > 15){
			System.out.println("Sorry, we can't use the numbers length longer than 4bits.");
			return -1;
		}
		
		boolean[] binaryA = getBinaryFromDecimal(numA, 4);
		boolean[] binaryB = getBinaryFromDecimal(numB, 4);
		
		ha01.setInput(binaryA[0], binaryB[0]);
		fa01.setInput(binaryA[1], binaryB[1], ha01.getCarry());
		fa02.setInput(binaryA[2], binaryB[2], fa01.getCarryOut());
		fa03.setInput(binaryA[3], binaryB[3], fa02.getCarryOut());
		
		int sum = 0;
		sum += (ha01.getSum() ? 1 : 0);
		sum += (fa01.getSum() ? 2 : 0);
		sum += (fa02.getSum() ? 4 : 0);
		sum += (fa03.getSum() ? 8 : 0);
		
		return sum;
	}