1、2、3、4、5、6......N连续整数相加

	public static int execute(int num){
		
		int result = 0;
		if(num % 2 == 0){
			result = num/2*num+num/2;
		}
		else{
			result = num/2*num+num%2*num;
		}
		return result;
	}