#include <bits/stdc++.h>
using namespace std;using ll=int_fast64_t;using ld=long double;using pll=pair<ll,ll>;constexpr ll INF=1LL<<60,MOD=1e9+7;//998244353;
void solve();int main(){cin.tie(nullptr);ios::sync_with_stdio(false);cout<<fixed<<setprecision(10);solve();return 0;}
#define SELECTOR(_1,_2,_3,_4,SELECT,...) SELECT
#define rep(...) SELECTOR(__VA_ARGS__,_rep2,_rep1,_rep0)(__VA_ARGS__)
#define _rep0(i,n) for(ll i=0;i<n;++i)
#define _rep1(i,k,n) for(ll i=k;i<n;++i)
#define _rep2(i,k,n,d) for(ll i=k;d>0?i<n:i>n;i+=d)
#define endl "\n"
#ifdef __LOCAL
#include "ostreams.h"
#endif
template<class T> inline bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}return 0;}
template<class T> vector<T> make_vector(size_t a,T b){return vector<T>(a,b);}
template<class... Ts> auto make_vector(size_t a,Ts... ts){return vector<decltype(make_vector(ts...))>(a,make_vector(ts...));}
void print(){cerr<<endl;} template<class T,class... Ts> void print(const T& a,const Ts&... ts){cerr<<a<<' ';print(ts...);}

template<ll MOD>
class Modint{
private:
    ll x;
public:
    constexpr Modint(ll v = 0) : x(v % MOD + (v >= 0 ? 0 : MOD)) {}
    constexpr Modint operator+(const Modint &rhs) const {return Modint(*this) += rhs;}
    constexpr Modint operator-(const Modint &rhs) const {return Modint(*this) -= rhs;}
    constexpr Modint operator*(const Modint &rhs) const {return Modint(*this) *= rhs;}
    constexpr Modint operator/(const Modint &rhs) const {return Modint(*this) /= rhs;}
    constexpr Modint operator+=(const Modint &rhs) {x += rhs.x; if(x >= MOD) x -= MOD; return *this;}
    constexpr Modint operator-=(const Modint &rhs) {x -= rhs.x; if(x < 0) x += MOD; return *this;}
    constexpr Modint operator*=(const Modint &rhs) {(x *= rhs.x) %= MOD; return *this;}
    constexpr Modint operator/=(const Modint &rhs) {return *this *= pow(rhs, -1);}
    template<class T> constexpr explicit operator T() const {return x;}
    constexpr static Modint pow(Modint a, ll p){
        if(p < 0){
            ll b = MOD, u = 1, v = 0;
            while(b){ll t = a.x / b; a.x -= t * b; a.x += b; b = a.x - b; a.x -= b; u -= t * v; u += v; v = u - v; u -= v;}
            a = u; p *= -1;}
        Modint res = 1;
        while(p){if(p & 1) res *= a; a *= a; p >>= 1;}
        return res;
    }
    constexpr void from_stream(istream &st) {st >> x;}
    constexpr void to_stream(ostream &st) const {st << x;}
};
template<ll MOD, class T> constexpr Modint<MOD> operator+(T a, Modint<MOD> b){return (Modint<MOD>)a + b;}
template<ll MOD, class T> constexpr Modint<MOD> operator-(T a, Modint<MOD> b){return (Modint<MOD>)a - b;}
template<ll MOD, class T> constexpr Modint<MOD> operator*(T a, Modint<MOD> b){return (Modint<MOD>)a * b;}
template<ll MOD, class T> constexpr Modint<MOD> operator/(T a, Modint<MOD> b){return (Modint<MOD>)a / b;}
template<ll MOD> constexpr istream& operator>>(istream &st, Modint<MOD> &a){a.from_stream(st); return st;}
template<ll MOD> constexpr ostream& operator<<(ostream &st, const Modint<MOD> &a){a.to_stream(st); return st;}
using mint = Modint<MOD>;

void solve(){
    ll n, k; cin >> n >> k;
    mint res = 0;

    rep(i, k, n + 2){
        // left : 0 + 1 + ... + (i - 1)
        // right : n - i + 1 + ... + n
        ll left = i * (i - 1) / 2;
        ll right = i * (2 * n - i + 1) / 2;
        res += right - left + 1;
    }
    cout << res << endl;
}

Measured memory_bytes: 3652