#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define sz(x) int(x.size())
using namespace std;
typedef long long ll;
typedef pair<int, int> P;

const ll INF = 1LL << 60;

const int mod = 1000000007;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x=0):x((x%mod+mod)%mod){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;}
  mint operator+(const mint a) const { return mint(*this) += a;}
  mint operator-(const mint a) const { return mint(*this) -= a;}
  mint operator*(const mint a) const { return mint(*this) *= a;}
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod-2);}
  mint& operator/=(const mint a) { return *this *= a.inv();}
  mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, const mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}

struct combination {
  vector<mint> fact, ifact;
  combination(int n):fact(n+1),ifact(n+1) {
    assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i;
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n]*ifact[k]*ifact[n-k];
  }
};

ll N, K;
int main() {
    cin >> N >> K;

    // combination comb = combination(3 * 10e5);
    // cout << comb(4, 2) << endl;
    vector<ll> sum(N + 2);
    rep(i, N + 1) {
        sum[i + 1] = sum[i] + i;
    }

    // rep(i, N + 2) {
    //     cout << sum[i] << endl;
    // }

    mint ans = 0;
    for (int i = K; i <= N; i++) {
        // cout << i << " " << sum[i] << " " << sum[N + 1] - sum[N - i] << endl;
        // cout<< sum[N + 1] - sum[N - i] << " " << sum[i] << endl;
        ll start = sum[i];
        ll end = sum[N + 1] - sum[N - i + 1];
        // cout << start << " " << end << endl;
        // cout << end - start + 1 << endl;
        ans += end - start + 1;
    }
    ans += 1;
    cout << ans << endl;
}