//
// ABC163D
// URL : https://atcoder.jp/contests/abc162/tasks/abc163_d
// 
using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;

namespace AtCoder
{
    class ABC163D
    {
        public static readonly long MOD_CONST = (long)Math.Pow(10, 9) + 7;
        static void Main(string[] args)
        {
            preprocess();
            // 整数配列の入力
            long[] inputLongArray = Console.ReadLine().Split(' ').Select(_inputStr => long.Parse(_inputStr)).ToArray();
            long N = inputLongArray[0];
            long K = inputLongArray[1];

            long ans = 0;
            var allSum = AggregateSum(N);
            for (var i = K; i <= N+1; ++i)
            {
                //10^100部分は無視して考える
                long minSum = AggregateSum(i-1);//0,1,...i-1までの和
                long maxSum = allSum - AggregateSum(N - i);//N-i, ..., Nまでの和
                long cnt = maxSum - minSum + 1;
                ans = ans + cnt;
                ans = ans % MOD_CONST;//毎回MODをとってもいい
            }


            Console.WriteLine(ans.ToString());
            Console.Out.Flush();
        }
        /// <summary>
        /// 累積和
        /// ただし初項1, 公差+1(1,2,3...と増加する)の場合
        /// </summary>
        /// <param name="x">求めたいところ</param>
        /// <returns>初項からxまで足した値</returns>
        static long AggregateSum(long x)
        {
            return (long)(x * (x + 1) / 2);
        }

        //---------------------------------------------------------------------------------
        /// <summary>
        /// 
        /// </summary>
        public static void preprocess()
        {
            //出力高速化
            var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
        }


        /// <summary>
        /// 与えられた数が素数かどうかを計算する
        /// </summary>
        /// <param name="num">対象数</param>
        /// <returns>true:素数, false:素数ではない(合成数)</returns>
        public static bool isPrime(int num)
        {
            if (num < 2) return false;
            else if (num == 2) return true;
            else if (num % 2 == 0) return false;

            double sqrtNum = Math.Sqrt(num);
            for (int i = 3; i <= sqrtNum; i += 2)
            {
                if (num % i == 0)
                {
                    return false;
                }
            }
            return true;
        }

        /// <summary>
        /// 順列mPnを計算する
        /// </summary>
        /// <param name="m"></param>
        /// <param name="n"></param>
        /// <returns></returns>
        public static long Permutation(long m, long n)
        {
            long ret = 1;
            for(var i = 0; i < n; ++i)
            {
                ret *= m - i;
            }
            return ret;
        }
        /// <summary>
        /// 組み合わせmCnを計算する
        /// </summary>
        /// <param name="m"></param>
        /// <param name="n"></param>
        /// <returns></returns>
        public static long Combination(long m, long n)
        {
            if(m == n || n == 0)
            {
                return 1;
            }
            long ans = 1;
            for(var i = 1; i <= n; ++i)
            {
                ans = ans * (m - i + 1) / i;
            }
            return ans;
        }

        static long Gcd(long m, long n)
        {
            if (n == 0) return m;
            return Gcd(n, m % n);
        }

        static long Lcm(long m, long n)
        {
            var gcd = Gcd(m, n);
            //return (m * n) / gcd;
            return m / gcd * n;//桁あふれ対策
        }
    }
}



Measured memory_bytes: 28560