#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
#define int ll

template<typename T1,typename T2> inline void chmin(T1 &a, T2 b){ if(a > b) a = b; }
template<typename T1,typename T2> inline void chmax(T1 &a, T2 b){ if(a < b) a = b; }

#define REP(i,n) for(int i=0;i<n;++i)
#define SORT(name) sort(name.begin(), name.end())
#define ZERO(p) memset(p, 0, sizeof(p))
#define MINUS(p) memset(p, -1, sizeof(p))
#if 1
#  define DBG(fmt, ...) printf(fmt, ##__VA_ARGS__)
#else
#  define DBG(fmt, ...)
#endif

const ll LLINF = (1LL<<60);
const int INF = (1LL<<30);
const double DINF = std::numeric_limits<double>::infinity();
const int MOD = 1000000007;
const int MAX_N = 100010;

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, t;
      while(b > 0) {
          t = a / b;
          swap(a -= t * b, b);
          swap(u -= t * v, v);
      }
      return ModInt(u);
  }

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

  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 >;

template< typename T >
class CumulativeSum
{
public:
    CumulativeSum() {}
    CumulativeSum(int sz) : m_Data(sz, T(0)) {};

    void Init(int sz) { m_Data.assign(sz, T(0)); }

    // k に x を加える O(1)
    void Add(int k, T x) {
        assert(static_cast<int>(m_Data.size()) >= k);
        if(static_cast<int>(m_Data.size()) <= k) { m_Data.push_back(x); }
        else { m_Data[k] = (m_Data[k] + x); }
    }

    // 累積和の構築 O(m_Data.size())
    void Build() {
        for(int i = 1; i < static_cast<int>(m_Data.size()); i++) {
            m_Data[i] = (m_Data[i] + m_Data[i - 1]);
        }
    }

    // 区間 [0, k] の和を返す O(1)
    // 閉区間なので k が含まれることに注意
    T Query(int k) {
        if(k < 0) { return T(0); }
        return (m_Data[min(k, static_cast<int>(m_Data.size()) - 1)]);
    }

    // 区間 [l, h] の和を返す O(1)
    // 閉区間なので k が含まれることに注意
    T Query(int l, int h) {
        return (this->Query(h) - this->Query(l-1));
    }
private:
    vector< T > m_Data;
};


signed main() {
    cin.tie(0); cout.tie(0);
    ios::sync_with_stdio(false);

    int N, K;
    cin >> N >> K;

    CumulativeSum<int> cs;
    REP(i, N + 10) {
        cs.Add(i, i);
    }
    cs.Build();

    modint ans(0);
    for(int i = K; i <= N + 1; ++i) {
        int c_min = cs.Query(0, i-1);
        int c_max = cs.Query(N - i + 1, N);
        modint cand(c_max - c_min + 1);
        //DBG("c_min: %lld c_max: %lld\n", c_min, c_max);
        ans += cand;
    }
    cout << ans << endl;

    return 0;
}


Measured memory_bytes: 5324