/*                         _
                        _ooOoo_
                       o8888888o
                       88" . "88
                       (| -_- |)
                       O\  =  /O
                    ____/`---'\____
                  .'  \\|     |//  `.
                 /  \\|||  :  |||//  \
                /  _||||| -:- |||||_  \
                |   | \\\  -  /'| |   |
                | \_|  `\`---'//  |_/ |
                \  .-\__ `-. -'__/-.  /
              ___`. .'  /--.--\  `. .'___
           ."" '<  `.___\_<|>_/___.' _> \"".
          | | :  `- \`. ;`. _/; .'/ /  .' ; |
          \  \ `-.   \_\_`. _.'_/_/  -' _.' /
===========`-.`___`-.__\ \___  /__.-'_.'_.-'================

                  Please give me AC.
*/

#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <numeric>
#include <string>
#include <sstream>
#include <complex>
#include <bitset>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <deque>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <chrono>
#include <random>

using namespace std;

using int64 = long long;
using uint64 = unsigned long long;
using vi = vector<int>;
using vl = vector<int64>;
using pii = pair<int, int>;
using pll = pair<int64, int64>;

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define all(v) (v).begin(), (v).end()
#define print(x) cout << (x) << '\n'
#define print2(x, y) cout << (x) << ' ' << (y) << '\n'
#define print3(x, y, z) cout << (x) << ' ' << (y) << ' ' << (z) << '\n'
#define printn(v) rep(i, (v).size() - 1) cout << (v)[i] << ' '; cout << (v)[n - 1] << '\n';
#define debug(x) cerr << #x << ": " << (x) << '\n'
#define debug2(x, y) cerr << #x << ": " << (x) << ", " << #y << ": " << (y) << '\n'
#define debug3(x, y, z) cerr << #x << ": " << (x) << ", " << #y << ": " << (y) << ", " << #z << ": " << (z) << '\n'
#define dbg(v) for (size_t _ = 0; _ < v.size(); ++_){cerr << #v << "[" << _ << "] : " << v[_] << '\n';}
// constant
const int INF = (1<<30) - 1;
const int64 INF64 = (1LL<<62) - 1;

template<typename T> T gcd(T a, T b) {
    if (a < b) return gcd(b, a);
    T r;
    while ((r = a % b)) {
        a = b;
        b = r;
    }
    return b;
}

template<typename T> T lcm(const T a, const T b) {
    return a / gcd(a, b) * b;
}

template<typename T> bool chmin(T& a, const T& b) {
    if (a > b) return a = b, true; else return false;
}

template<typename T> bool chmax(T& a, const T& b) {
    if (a < b) return a = b, true; else return false;
}

// End of template.

// Begin Mod
template<typename T, T mod_, bool is_prime = true>
class Mod {
public:
    using Self = Mod<T, mod_, is_prime>;
    T value;
    static constexpr T mod = mod_;
    constexpr Mod() : value() {}
    constexpr Mod(T x) : value() { value = x % mod; }
    explicit constexpr operator T&() { return value; }
    constexpr Self operator +(Self const x) const { return (value + x.value) % mod; }
    constexpr Self operator *(Self const x) const { return (value * x.value) % mod; }
    constexpr Self operator -(Self const x) const { return (mod + value - x.value) % mod; }
    constexpr Self operator /(Self const x) const { return (value * x.inv().value) % mod; }
    constexpr Self operator +=(Self const x) { return value = (value + x.value) % mod; }
    constexpr Self operator *=(Self const x) { return value = (value * x.value) % mod; }
    constexpr Self operator -=(Self const x) { return value = (mod + value - x.value) % mod; }
    constexpr Self operator /=(Self const x) { return value = (value * x.inv().value) % mod; }
    constexpr Self inv() const {
        T a = value, b = mod, u = 1, v = 0;
        while (b) {
            T t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        u %= mod;
        if (u < 0) u += mod;
        return u;
    }
    constexpr Self pow(int e) const {
        if (e < 0) return inv().pow(-e);
        if (is_prime) e %= mod - 1;
        Self base = value;
        Self res = 1;
        while (e > 0) {
            if (e & 1) res *= base;
            base *= base;
            e >>= 1;
        }
        return res;
    }
};

template<typename T, T mod>
istream& operator>>(istream& stream, Mod<T, mod>& m) {
    return stream >> m.value;
}

template<typename T, T mod>
ostream& operator<<(ostream& stream, const Mod<T, mod>& m) {
    return stream << m.value;
}
// End Mod

constexpr int64 mod = 1e9 + 7;
using M = Mod<int64, mod>;

int64 s(int64 n) {
    return n * (n + 1) / 2;
}

int main() {
    cout << fixed << setprecision(15);
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    // cin.read(buf, sizeof buf); // 注意: ./a.out < in か pbp | ./a.out で入力すること

    int64 n, k;
    cin >> n >> k;

    M ans = 0;

    for (int i = k; i <= n + 1; ++i) {
        ans += 1 + (s(n) - s(n - i)) - (s(i-1));
    }

    print(ans);

    return 0;
}



Measured memory_bytes: 3652