#pragma GCC optimize ("O3")
#include "bits/stdc++.h"

using namespace std;
using ll = long long int;

#define all(v) (v).begin(),(v).end()
#define repeat(cnt,l) for(typename remove_const<typename remove_reference<decltype(l)>::type>::type cnt={};(cnt)<(l);++(cnt))
#define rrepeat(cnt,l) for(auto cnt=(l)-1;0<=(cnt);--(cnt))
#define iterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);++(cnt))
#define diterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);--(cnt))
const long long MD = 1000000007ll; const long double PI = 3.1415926535897932384626433832795L;
template<typename T1, typename T2> inline ostream& operator <<(ostream &o, const pair<T1, T2> p) { o << '(' << p.first << ':' << p.second << ')'; return o; }
template<typename T> inline T& chmax(T& to, const T& val) { return to = max(to, val); }
template<typename T> inline T& chmin(T& to, const T& val) { return to = min(to, val); }
void bye(string s, int code = 0) { cout << s << endl; exit(code); }
mt19937_64 randdev(8901016);
template<typename T, typename Random = decltype(randdev), typename enable_if<is_integral<T>::value>::type* = nullptr>
inline T rand(T l, T h, Random& rand = randdev) { return uniform_int_distribution<T>(l, h)(rand); }
template<typename T, typename Random = decltype(randdev), typename enable_if<is_floating_point<T>::value>::type* = nullptr>
inline T rand(T l, T h, Random& rand = randdev) { return uniform_real_distribution<T>(l, h)(rand); }

template <typename I>
struct MyRangeFormat{ I b,e; MyRangeFormat(I _b, I _e):b(_b),e(_e){} };
template<typename I>
static ostream& operator<<(ostream& o, const MyRangeFormat<I>& f) {
  o << "[ "; iterate(i,f.b,f.e) o<<*i<<' ';
  return o << ']';
}
template <typename I>
struct MyMatrixFormat{
  const I& p; long long n, m;
  MyMatrixFormat(const I& _p, long long _n, long long _m):p(_p),n(_n),m(_m){}
};
template<typename I>
static ostream& operator<<(ostream& o, const MyMatrixFormat<I>& f) {
  o<<'\n';
  repeat(i,(f.n)) {
    repeat(j,f.m) o<<f.p[i][j]<<' ';
    o<<'\n';
  }
  return o;
}
struct LOG_t { ~LOG_t() { cout << endl; } };
#define LOG (LOG_t(),cout<<'L'<<__LINE__<<": ")
#define FMTA(m,w) (MyRangeFormat<decltype(m+0)>(m,m+w))
#define FMTR(b,e) (MyRangeFormat<decltype(e)>(b,e))
#define FMTV(v) FMTR(v.begin(),v.end())
#define FMTM(m,h,w) (MyMatrixFormat<decltype(m+0)>(m,h,w))

#if defined(_WIN32) || defined(_WIN64)
#define getc_x _getc_nolock
#define putc_x _putc_nolock
#elif defined(__GNUC__)
#define getc_x getc_unlocked
#define putc_x putc_unlocked
#else
#define getc_x getc
#define putc_x putc
#endif
#define isvisiblechar(c) (0x21<=(c)&&(c)<=0x7E)
class MaiScanner {
  FILE* fp_;
public:
  inline MaiScanner(FILE* fp):fp_(fp){}
  template<typename T> void input_integer(T& var) noexcept {
    var = 0; T sign = 1;
    int cc = getc_x(fp_);
    for (; cc < '0' || '9' < cc; cc = getc_x(fp_))
      if (cc == '-') sign = -1;
    for (; '0' <= cc && cc <= '9'; cc = getc_x(fp_))
      var = (var << 3) + (var << 1) + cc - '0';
    var = var * sign;
  }
  inline int c() noexcept { return getc_x(fp_); }
  // template<typename T, enable_if_t<is_integral<T>::value>>
  inline MaiScanner& operator>>(int& var) noexcept { input_integer<int>(var); return *this; }
  inline MaiScanner& operator>>(long long& var) noexcept { input_integer<long long>(var); return *this; }
  inline MaiScanner& operator>>(string& var) {
    int cc = getc_x(fp_);
    for (; !isvisiblechar(cc); cc = getc_x(fp_));
    for (; isvisiblechar(cc); cc = getc_x(fp_))
      var.push_back(cc);
    return *this;
  }
  template<typename IT> inline void in(IT begin, IT end) { for (auto it = begin; it != end; ++it) *this >> *it; }
};
class MaiPrinter {
  FILE* fp_;
public:
  inline MaiPrinter(FILE* fp):fp_(fp){}
  template<typename T>
  void output_integer(T var) noexcept {
    if (var == 0) { putc_x('0', fp_); return; }
    if (var < 0)
      putc_x('-', fp_),
      var = -var;
    char stack[32]; int stack_p = 0;
    while (var)
      stack[stack_p++] = '0' + (var % 10),
      var /= 10;
    while (stack_p)
      putc_x(stack[--stack_p], fp_);
  }
  inline MaiPrinter& operator<<(char c) noexcept { putc_x(c, fp_); return *this; }
  inline MaiPrinter& operator<<(int var) noexcept { output_integer<int>(var); return *this; }
  inline MaiPrinter& operator<<(long long var) noexcept { output_integer<long long>(var); return *this; }
  inline MaiPrinter& operator<<(char* str_p) noexcept { while (*str_p) putc_x(*(str_p++), fp_); return *this; }
  inline MaiPrinter& operator<<(const string& str) {
    const char* p = str.c_str();
    const char* l = p + str.size();
    while (p < l) putc_x(*p++, fp_);
    return *this;
  }
  template<typename IT> void join(IT begin, IT end, char sep = ' ') { for (bool b = 0; begin != end; ++begin, b = 1) b ? *this << sep << *begin : *this << *begin; }
};
MaiScanner scanner(stdin);
MaiPrinter printer(stdout);

template <int MaxN, long long Mod>
class Combinatorics {
  using value_type = long long;
  value_type fact_[MaxN + 1];
  // value_type inv_[MaxN + 1]; // iranai

 public:
  constexpr value_type pow(value_type x, value_type p) const {
    value_type y = 1;
    x = x % Mod;
    for (; 0 < p; p >>= 1) {
      if (p & 1)
        y = y * x % Mod;
      x = x * x % Mod;
    }
    return y;
  }

  constexpr Combinatorics() : fact_() {
    fact_[0] = 1;
    fact_[1] = 1;
    for (value_type n = 2; n <= MaxN; ++n)
      fact_[n] = (fact_[n - 1] * n) % Mod;
    // inv_[Max] := calculate;
    // iterate => inv_[i] = inv_[i+1] * (i+1) % MD;
  }
  constexpr value_type fact(int n) const { return fact_[n]; }

  constexpr value_type inv(value_type n) const { return pow(n, MD - 2); }

  constexpr value_type nPr(value_type n, value_type r) const {
    if (r < 0 || n < r)
      return 0;
    return fact_[n] * inv(fact_[n - r]) % MD;
  }
  constexpr value_type nCr(value_type n, value_type r) const {
    if (n < r)
      return 0;
    return ((fact_[n] * inv(fact_[n - r]) % MD) * inv(fact_[r])) % MD;
  }
  constexpr value_type nHr(value_type n, value_type r) const {
    if (n == 0 && r == 0)
      return 1;
    if (n == 0)
      return 0;
    return nCr(n - 1 + r, n - 1);
  }
};
//

int A[200010];

//

Combinatorics<200010, MD> wkm;

ll sum(ll x) {
  return (x)*(x+1)/2;
}


int main() {
  
  ll N, K;
  scanner >> N >> K;
  
  ll total = 0;
  ll num = 1, den = 1;
  iterate(i, K, N+2) {
    // num = num * (N+2-i) % MD;
    // den = den * (i) % MD;
    // if (i < K) continue;
    // ll ncr = num * pow_md(den, MD - 2, MD) % MD;
    ll ncr = 1;//wkm.nCr(N+1, i);
    // LOG << sum(N) - sum(N-i);
    // LOG << sum(i-1);
    ll rng = sum(N)-sum(N-i) - sum(i-1) + 1;
    // LOG << rng;
    total += rng*ncr;
    total %= MD;
  }
  
  cout << total << endl;
  
  return 0;
}


Measured memory_bytes: 3704