#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
typedef pair<int, P> P1;
typedef pair<P, P> P2;
#define pu push
#define pb push_back
#define mp make_pair
#define eps 1e-7
#define INF 1000000000
#define mod 1000000007
#define fi first
#define sc second
#define rep(i, x) for (long long i = 0; i < x; i++)
#define repn(i, x) for (long long i = 1; i <= x; i++)
#define SORT(x) sort(x.begin(), x.end())
#define ERASE(x) x.erase(unique(x.begin(), x.end()), x.end())
#define POSL(x, v) (lower_bound(x.begin(), x.end(), v) - x.begin())
#define POSU(x, v) (upper_bound(x.begin(), x.end(), v) - x.begin())
vector<pair<string, P> > vec;
// vector<vector<int>> data(3, vector<int>(4));

template <signed M, unsigned T>
struct mod_int {
    constexpr static signed MODULO = M;
    constexpr static unsigned TABLE_SIZE = T;

    signed x;

    mod_int() : x(0) {}

    mod_int(long long y)
        : x(static_cast<signed>(y >= 0 ? y % MODULO : MODULO - (-y) % MODULO)) {
    }

    mod_int(int y) : x(y >= 0 ? y % MODULO : MODULO - (-y) % MODULO) {}

    mod_int &operator+=(const mod_int &rhs) {
        if ((x += rhs.x) >= MODULO) x -= MODULO;
        return *this;
    }

    mod_int &operator-=(const mod_int &rhs) {
        if ((x += MODULO - rhs.x) >= MODULO) x -= MODULO;
        return *this;
    }

    mod_int &operator*=(const mod_int &rhs) {
        x = static_cast<signed>(1LL * x * rhs.x % MODULO);
        return *this;
    }

    mod_int &operator/=(const mod_int &rhs) {
        x = static_cast<signed>((1LL * x * rhs.inv().x) % MODULO);
        return *this;
    }

    mod_int operator-() const { return mod_int(-x); }

    mod_int operator+(const mod_int &rhs) const {
        return mod_int(*this) += rhs;
    }

    mod_int operator-(const mod_int &rhs) const {
        return mod_int(*this) -= rhs;
    }

    mod_int operator*(const mod_int &rhs) const {
        return mod_int(*this) *= rhs;
    }

    mod_int operator/(const mod_int &rhs) const {
        return mod_int(*this) /= rhs;
    }

    bool operator<(const mod_int &rhs) const { return x < rhs.x; }

    mod_int inv() const {
        assert(x != 0);
        if (x <= static_cast<signed>(TABLE_SIZE)) {
            if (_inv[1].x == 0) prepare();
            return _inv[x];
        } else {
            signed a = x, b = MODULO, u = 1, v = 0, t;
            while (b) {
                t = a / b;
                a -= t * b;
                std::swap(a, b);
                u -= t * v;
                std::swap(u, v);
            }
            return mod_int(u);
        }
    }

    mod_int pow(long long t) const {
        assert(!(x == 0 && t == 0));
        mod_int e = *this, res = mod_int(1);
        for (; t; e *= e, t >>= 1)
            if (t & 1) res *= e;
        return res;
    }

    mod_int fact() {
        if (_fact[0].x == 0) prepare();
        return _fact[x];
    }

    mod_int inv_fact() {
        if (_fact[0].x == 0) prepare();
        return _inv_fact[x];
    }

    mod_int choose(mod_int y) {
        assert(y.x <= x);
        return this->fact() * y.inv_fact() * mod_int(x - y.x).inv_fact();
    }

    static mod_int _inv[TABLE_SIZE + 1];

    static mod_int _fact[TABLE_SIZE + 1];

    static mod_int _inv_fact[TABLE_SIZE + 1];

    static void prepare() {
        _inv[1] = 1;
        for (int i = 2; i <= (int)TABLE_SIZE; ++i) {
            _inv[i] = 1LL * _inv[MODULO % i].x * (MODULO - MODULO / i) % MODULO;
        }
        _fact[0] = 1;
        for (unsigned i = 1; i <= TABLE_SIZE; ++i) {
            _fact[i] = _fact[i - 1] * int(i);
        }
        _inv_fact[TABLE_SIZE] = _fact[TABLE_SIZE].inv();
        for (int i = (int)TABLE_SIZE - 1; i >= 0; --i) {
            _inv_fact[i] = _inv_fact[i + 1] * (i + 1);
        }
    }
};

template <int M, unsigned F>
std::ostream &operator<<(std::ostream &os, const mod_int<M, F> &rhs) {
    return os << rhs.x;
}

template <int M, unsigned F>
std::istream &operator>>(std::istream &is, mod_int<M, F> &rhs) {
    long long s;
    is >> s;
    rhs = mod_int<M, F>(s);
    return is;
}

template <int M, unsigned F>
mod_int<M, F> mod_int<M, F>::_inv[TABLE_SIZE + 1];

template <int M, unsigned F>
mod_int<M, F> mod_int<M, F>::_fact[TABLE_SIZE + 1];

template <int M, unsigned F>
mod_int<M, F> mod_int<M, F>::_inv_fact[TABLE_SIZE + 1];

template <int M, unsigned F>
bool operator==(const mod_int<M, F> &lhs, const mod_int<M, F> &rhs) {
    return lhs.x == rhs.x;
}

template <int M, unsigned F>
bool operator!=(const mod_int<M, F> &lhs, const mod_int<M, F> &rhs) {
    return !(lhs == rhs);
}

const int MF = 1000010;
const int MOD = 1000000007;

using mint = mod_int<MOD, MF>;

mint binom(int n, int r) {
    return (r < 0 || r > n || n < 0) ? 0 : mint(n).choose(r);
}

mint fact(int n) { return mint(n).fact(); }

mint inv_fact(int n) { return mint(n).inv_fact(); }

void solve(long long N, long long K) {
    mint res = 0;
    mint s = 0, t = 0;
    repn(i, N + 1) {
        s += i - 1;
        t += N + 1 - i;
        if (i < K) continue;
        res += t - s + 1;
    }
    cout << res << endl;
}

int main() {
    long long K;
    long long N;
    scanf("%lld", &N);
    scanf("%lld", &K);
    solve(N, K);
    return 0;
}


Measured memory_bytes: 15492