#include <bits/stdc++.h>
#define cout16 cout << setprecision(16) 
#define rep(i,n) for(int i=0;i<n;i++ )
#define rep2(i,f,n) for(int i=f;i<n;i++ )
#define SORT(A) sort(A.begin(),A.end())
#define REV(A) reverse(A.begin(),A.end())
typedef long long int ll;
using vi = std::vector<int>;
using vvi = std::vector<std::vector<int>>;
using vll = std::vector<ll>;
using vvll = std::vector<std::vector<ll>>;
using P = std::pair<int,int>;
using vp = std::vector<P>;
using namespace std;
#define INF 1001001001
#define LL_INF 1001001001001001001
#define fi first
#define se second
// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const int mod = 1000000007;
//const int mod = 998244353;
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;}
int main(void) {
	ll n,k; cin >> n >> k;
	mint ans = 0;
	for(ll i=k; i<=n+1; i++){
		ll mn = i*(i-1)/2;
		ll mx = n*(n+1)/2 - (n-i)*(n-i+1)/2;
		ans += mx-mn+1;
	}
	cout << ans << endl;
}
