#include <iostream>
#include <string>
#include <vector>
#include <iomanip>
#include <algorithm>
#include <stack>

using std::cin;
using std::cout;
using std::pair;
using std::cerr;
using std::string;
using std::vector;
//region define/typedef
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define FORR(i, a, b) for (int (i) = (b); (i) >= (b); (i)--)
#define rep(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define rep1(i, n) for (int (i) = 1; (i) <= (n); (i)++)
#define repr(i, n) for (int (i) = (n)-1; (i) >= 0; (i)--)
#define repr1(i, n) for (int (i) = (n); (i) > 0; (i)--)
#define pb push_back
#define mp std::make_pair
#define mt std::make_tuple
#define outif(b, t, f) cout << ((b) ? (t) : (f)) << endl
#define bsort(vec) std::sort((vec).begin(), (vec).end())
#define rsort(vec) std::sort((vec).rbegin(), (vec).rend())
#define all(vec) (vec).begin(), (vec).end()
#define even(i) (!(i & 1))
#define odd(i) (i & 1)
#define sz(x) (int((x).size()))
#define mset(v, n) std::memset((v), n, sizeof(v))
#define setminus(v) mset(v, -1)
#define setzero(v) mset(v, 0)
#define BIT(N) (1LL << (N))
using ll = long long;
using lld = long double;
using uint = unsigned int;
using vint = vector<int>;
using vlong = vector<ll>;
using vstr = vector<string>;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pll = pair<ll, ll>;
using vpii = vector<pii>;
using vpil = vector<pil>;
using vpll = vector<pll>;
//endregion
//region methods/operator
const string endl = "\n";
ll parse(const string &num) {
  std::stringstream ss;
  ss << num << std::flush;
  ll n;
  ss >> n;
  return n;
}

string to_string(const ll n) {
  std::stringstream ss;
  ss << n << std::flush;
  return ss.str();
}

vector<string> split(const string &s, const string &delim) {
  vector<string> res;
  auto pos = 0;
  while (true) {
    const int found = s.find(delim, pos);
    if (found >= 0) {
      res.push_back(s.substr(pos, found - pos));
    } else {
      res.push_back(s.substr(pos));
      break;
    }
    pos = found + delim.size();
  }
  return res;
}

template<typename T>
string join(vector<T> &vec, const string &sep = " ") {
  size_t size = vec.size();
  if (size == 0)
    return "";
  std::stringstream ss;
  for (int i = 0; i < size - 1; i++) {
    ss << vec[i] << sep;
  }
  ss << vec[size - 1];
  return ss.str();
}

template<typename T>
std::istream &operator>>(std::istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}

template<typename T>
void print(T t) {
  cout << t << endl;
}

constexpr ll powmod(ll a, ll b, ll p) {
  ll res = 1;
  while (b > 0) {
    if (b % 2)
      res = res * a % p;
    a = a * a % p;
    b >>= 1;
  }
  return res;
}

constexpr ll gcd(ll a, ll b) {
  if (a < b)
    gcd(b, a);
  ll r = a % b;
  while (r) {
    a = b;
    b = r;
    r = a % b;
  }
  return b;
}

constexpr ll lcm(const ll a, const ll b) { return a / gcd(a, b) * b; }

template<class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template<class T>
bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

//endregion
//region initialize

struct iii {
    iii() {
      cin.tie(nullptr);
      std::ios::sync_with_stdio(false);
      cout << std::fixed << std::setprecision(16);
    }
} init;

//endregion

int main() {
  int N, K;
  scanf("%d%d",&N,&K);

  long long int ans = 0;
  const int mod = 1e9+7;

  FOR(i,K,N+2){
    ll min = i * ll(i - 1) / 2;
    ll max = N * ll(N + 1) / 2 - ll(N - i) * (N - i + 1) / 2;
    ans += max - min + 1;
    ans %= mod;
  }

  printf("%lld", ans);

  return 0;
}


Measured memory_bytes: 3824