#include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <cstring>
#include <iomanip>
#include <numeric>
#include <cmath>
#include <cassert>
#include <queue>
#include <map>
#include <set>
using namespace std;
using ll = long long;
const int INF = 1<<30;
const int MOD = (int)1e9 + 7;
const int MAX_N = (int)1e5 + 5;
#define debug(x) cout << #x << ": " << x << endl
template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2>& p) { os << p.first << " " << p.second; return os; }
template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v) { for(int i = 0; i < (int) v.size(); i++) os << v[i] << (i + 1 != v.size() ? " " : ""); return os; }

template <int mod>
struct ModInt
{
    int x;
    ModInt() : x(0) {}
    ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

    ModInt &operator+=(const ModInt &p)
    {
        if ((x += p.x) >= mod)
        {
            x -= mod;
        }
        return *this;
    }
    ModInt &operator-=(const ModInt &p)
    {
        if ((x += mod - p.x) >= mod)
        {
            x -= mod;
        }
        return *this;
    }
    ModInt &operator*=(const ModInt &p)
    {
        x = (int)(1LL * x * p.x % mod);
        return *this;
    }
    ModInt &operator/=(const ModInt &p)
    {
        *this *= p.inverse();
        return *this;
    }

    ModInt operator-() const { return ModInt(-x); }
    ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }
    ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }
    ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }
    ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

    bool operator==(const ModInt &p) const { return x == p.x; }
    bool operator!=(const ModInt &p) const { return x != p.x; }

    ModInt inverse() const
    {
        int a = x, b = mod, u = 1, v = 0;
        while (b > 0)
        {
            int t = a / b;
            swap(a -= t * b, b);
            swap(u -= t * v, v);
        }
        return ModInt(u);
    }

    ModInt pow(int64_t n) const
    {
        ModInt res(1), mul(x);
        while (n > 0)
        {
            if (n & 1)
            {
                res *= mul;
            }
            mul *= mul;
            n >>= 1;
        }
        return res;
    }

    friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; }
    friend istream &operator>>(istream &is, ModInt &a)
    {
        int64_t t;
        is >> t;
        a = ModInt<mod>(t);
        return (is);
    }

    static int get_mod() { return mod; }
};
using modint = ModInt<MOD>;

void solve()
{
    ll n, k; cin >> n >> k;
    vector<modint> A(n + 1);
    for(int i = 0; i <= n; i++) A[i] = i;
    vector<modint> sum((int)A.size() + 1, 0);
    for(int i = 0; i < (int)A.size(); i++)
    {
        sum[i + 1] = sum[i] + A[i];
    }

    modint ans = 0;
    for(ll i = k; i <= n + 1; i++)
    {
        modint M = sum.back() - sum[(ll)sum.size() - i - 1];
        modint m = sum[i];
        ans += M - m + 1LL;
    }
    cout << ans << endl;
}

signed main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}

Measured memory_bytes: 4756