/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author champon
 */

#include <iostream>
#include <fstream>
#include <bits/stdc++.h>
#define se cout << "test ok" << endl;
#define sp << " " <<
#define enl "\n"
using namespace std;
using ll=long long;
using ld=long double;
using vi = vector<int>;
using vii = vector<vector<int>>;
using vl = vector<ll>;
using vll = vector<vector<ll>>;
using vlll = vector<vector<vector<ll>>>;
using vc = vector<char>;
using vcc = vector<vector<char>>;
using pi = pair<int, int>;
using pl = pair<ll, ll>;
ll mod = ll(1e9)+7;
ll inf = ll(1e18);
void bl(bool b, ostream& out=cout){ out << (b ? "Yes" : "No") << endl; }
void bl2(bool b, ostream& out=cout){ out << (b ? "YES" : "NO") << endl; }
template<typename T> inline bool chmax(T &a, T b){ if(a<b){a=b; return true;} return false; }
template<typename T> inline bool chmin(T &a, T b){ if(a>b){a=b; return true;} return false; }
int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
int dy[] = {0, 1, 0, -1, 1, -1, -1, 1};

#ifndef INCLUDE_DEBUG_HPP
#define INCLUDE_DEBUG_HPP

#include <iostream>
#include <vector>
#include <map>
using namespace std;

namespace dbg {
    using ll = long long;

    class Debug {
    public:
        Debug(){}
        template<typename T>
        void vd(vector<T> vec);
        template<typename T>
        void vd2(vector<vector<T>> vec);
        template<typename T>
        void ad(T *arr, ll n);
        template<typename T, size_t N>
        void ad2(T (&arr)[N], ll n);
        template<typename T>
        void md(T mp);
    };

    template<typename T>
    void Debug::vd(vector<T> vec) {
        for (auto vv : vec) cout << vv << " ";
        cout << endl;
    }

    template<typename T>
    void Debug::vd2(vector<vector<T>> vec) {
        for (auto vv : vec) {
            for (auto vvv : vv) cout << vvv << " ";
            cout << endl;
        }
    }

    template<typename T>
    void Debug::ad(T *arr, ll n) {
        for (int i = 0; i <= n; i++) cout << arr[i] << " ";
        cout << endl;
    }

    template<typename T, size_t N>
    void Debug::ad2(T (&arr)[N], ll n) {
        for (int i = 0; i <= N; i++) for (int j = 0; j <= n; j++) cout << arr[i][j] << " ";
        cout << endl;
    }

    template<typename T>
    void Debug::md(T mp) {
        cout << "key : value" << endl;
        for (auto const &m : mp) cout << m.first << " : " << m.second << endl;
        cout << endl;
    }

}

#endif //INCLUDE_DEBUG_HPP

using dbg::Debug;
Debug debug;

#ifndef INCLUDE_MINT_HPP
#define INCLUDE_MINT_HPP

namespace mint {

    using ll = long long;

    class Mint {
    public:
        ll v;
        ll mod;

        Mint(ll v=0, ll mod=ll(1e9)+7) : mod(mod), v((v % mod + mod) % mod) {}

        Mint operator-() const { return Mint(-v); }
        Mint operator+(const Mint rhs) const {
            Mint res(*this);
            return res += rhs;
        }
        Mint operator-(const Mint rhs) const {
            Mint res(*this);
            return res -= rhs;
        }
        Mint operator*(const Mint rhs) const {
            Mint res(*this);
            return res *= rhs;
        }
        Mint &operator+=(const Mint rhs) {
            if ((v += rhs.v) >= mod) v -= mod;
            return *this;
        }
        Mint &operator-=(const Mint rhs) {
            if ((v += mod - rhs.v) >= mod) v -= mod;
            return *this;
        }
        Mint &operator*=(const Mint rhs) {
            (v *= rhs.v) %= mod;
            return *this;
        }
        Mint pow(ll t) const {
            if (!t) return 1;
            Mint b = pow(t >> 1);
            b *= b;
            if (t & 1) b *= *this;
            return b;
        }
        Mint inv() const {
            return pow(mod - 2);
        }
        Mint &operator/=(const Mint rhs) {
            return (*this) *= rhs.inv();
        }
        Mint operator/(const Mint rhs) const {
            Mint res(*this);
            return res /= rhs;
        }
    };

}

#endif //INCLUDE_MINT_HPP

using mint::Mint;

class DSumOfLargeNumbers {
public:
	void solve(std::istream& in, std::ostream& out) {
	    ll n, k;
	    in >> n >> k;

        Mint res;
        for(ll i=k; i<=n; i++){
            Mint mx = n*(n+1)/2-(n-i+1)*(n-i)/2;
            Mint mi = i*(i-1)/2;
            res += mx-mi+1;
        }

        out << res.v+1 << enl;
	}
};


int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
	DSumOfLargeNumbers solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	solver.solve(in, out);
	return 0;
}


Measured memory_bytes: 3652