从n累加到m，n,m从键盘敲入，如何写呢？

public static void main(String[] args) throws Exception {        int[] arg = { 0, 0 };        for (int i = 0; i < 2; i++) {            System.out.print("输入第" + (i + 1) + "个数:");            DataInputStream di = new DataInputStream(System.in);            String num = di.readLine();            arg[i] = Integer.parseInt(num);        }        System.out.println(firstMethod(arg[0], arg[1]));        System.out.println(secondMethod(arg[0], arg[1]));    }    static int firstMethod(int start, int end) {        int sum = 0;        for (; start <= end; start++) {            sum += start;        }        return sum;    }    static int oneToAnum(int num) {        int k = ((1 + num) * num) / 2;        return k;    }    static int secondMethod(int first, int second) {        return oneToAnum(second) - oneToAnum(first - 1);    }