#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define all(x) (x).begin(),(x).end()
using namespace std;
using ll = long long;
using P = pair<int,int>;
template <class T> void chmin(T &a, const T &b) noexcept { if (b < a) a = b; }
template <class T> void chmax(T &a, const T &b) noexcept { if (a < b) a = b; }
void debug_out() { cout << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) { cout << H << " "; debug_out(T...); }
#ifdef _DEBUG
  #define debug(...) debug_out(__VA_ARGS__)
#else
  #define debug(...) 
#endif

const int mod = 1000000007;
// const int mod = 998244353;
struct mint {
  ll x;
  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, mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(15);
  ll n, k;
  cin >> n >> k;
  mint ans(0);
  mint itrmin = 0, itrmax = n;
  mint mini = 0, maxi = 0;
  rep(i,k) {
    mini += itrmin;
    maxi += itrmax;
    itrmin += 1;
    itrmax -= 1;
  }
  for (ll i = k; i <= n+1; ++i) {
    ans += maxi - mini + 1;
    mini += itrmin;
    maxi += itrmax;
    itrmin += 1;
    itrmax -= 1;
  }
  cout << ans << endl;
  return 0;
}