// Original C++ solution (slower):
#include <bits/stdc++.h>



#define rep(i,n) for(int i=0;i<(int)(n);i++)

#define FOR(i,n,m) for(int i=(int)(n); i<=(int)(m); i++)

#define RFOR(i,n,m) for(int i=(int)(n); i>=(int)(m); i--)

#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)

#define RITR(x,c) for(__typeof(c.rbegin()) x=c.rbegin();x!=c.rend();x++)

#define setp(n) fixed << setprecision(n)



template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }

template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }



#define ll long long

#define vll vector<ll>

#define vi vector<int>

#define pll pair<ll,ll>

#define pi pair<int,int>



#define all(a) (a.begin()),(a.end())

#define rall(a) (a.rbegin()),(a.rend())

#define fi first

#define se second

#define pb push_back

#define mp make_pair

#define ins insert



using namespace std;



//-------------------------------------------------

//--ModInt

//-------------------------------------------------

const ::std::uint_fast64_t MOD = 1e9+7;



class mint

{

private:

    using value_type = ::std::uint_fast64_t;

    value_type n;

public:

    mint():n(0){}

    mint(::std::int_fast64_t _n):n(_n<0 ? MOD-(-_n)%MOD : _n%MOD){}

    mint(const mint &m):n(m.n){}



    friend ::std::ostream& operator<<(::std::ostream &os, const mint &a){

		return os << a.n;

	}

    friend ::std::istream& operator>>(::std::istream &is, mint &a){

        value_type temp; is>>temp;

        a = mint(temp);

        return is;

    }



    mint& operator+=(const mint &m){n+=m.n; n=(n<MOD)?n:n-MOD; return *this;}

    mint& operator-=(const mint &m){n+=MOD-m.n; n=(n<MOD)?n:n-MOD; return *this;}

    mint& operator*=(const mint &m){n=n*m.n%MOD; return *this;}

    mint& operator/=(const mint &m){return *this*=m.inv();}

    mint& operator++(){return *this+=1;}

    mint& operator--(){return *this-=1;}



    mint operator+(const mint &m) const {return mint(*this)+=m;}

    mint operator-(const mint &m) const {return mint(*this)-=m;}

    mint operator*(const mint &m) const {return mint(*this)*=m;}

    mint operator/(const mint &m) const {return mint(*this)/=m;}

    mint operator++(int){mint t(*this); *this+=1; return t;}

    mint operator--(int){mint t(*this); *this-=1; return t;}



    bool operator==(const mint &m) const {return n==m.n;}

    bool operator!=(const mint &m) const {return n!=m.n;}

    mint operator-() const {return mint(MOD-n);}



    mint pow(value_type b) const {

        mint ret(1), m(*this);

        while(b){

            if (b & 1) ret*=m;

            m*=m;

            b>>=1;

        }

        return ret;

    }



    mint inv() const {return pow(MOD-2);}

};



//-------------------------------------------------



int main(void)

{

    cin.tie(0);

    ios::sync_with_stdio(false);

    int n,k; cin>>n>>k;

    mint ans=0;

    FOR(i,k,n+1){

        mint mini = mint(i-1)*i/2;

        mint maxi = mint(2*n-i+1)*i/2;

        ans+=maxi-mini+1;

    }

    cout<<ans<<"\n";

    return 0;

}


// Optimized solution to the same problem (faster):
#include <bits/stdc++.h>



#define rep(i,n) for(int i=0;i<(int)(n);i++)

#define FOR(i,n,m) for(int i=(int)(n); i<=(int)(m); i++)

#define RFOR(i,n,m) for(int i=(int)(n); i>=(int)(m); i--)

#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)

#define RITR(x,c) for(__typeof(c.rbegin()) x=c.rbegin();x!=c.rend();x++)

#define setp(n) fixed << setprecision(n)



template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }

template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }



#define ll long long

#define vll vector<ll>

#define vi vector<int>

#define pll pair<ll,ll>

#define pi pair<int,int>



#define all(a) (a.begin()),(a.end())

#define rall(a) (a.rbegin()),(a.rend())

#define fi first

#define se second

#define pb push_back

#define mp make_pair

#define ins insert



using namespace std;



//-------------------------------------------------

//--ModInt

//-------------------------------------------------

const ::std::uint_fast64_t MOD = 1e9+7;



class mint

{

private:

    using value_type = ::std::uint_fast64_t;

    value_type n;

public:

    mint():n(0){}

    mint(::std::int_fast64_t _n):n(_n<0 ? MOD-(-_n)%MOD : _n%MOD){}

    mint(const mint &m):n(m.n){}



    friend ::std::ostream& operator<<(::std::ostream &os, const mint &a){

		return os << a.n;

	}

    friend ::std::istream& operator>>(::std::istream &is, mint &a){

        value_type temp; is>>temp;

        a = mint(temp);

        return is;

    }



    mint& operator+=(const mint &m){n+=m.n; n=(n<MOD)?n:n-MOD; return *this;}

    mint& operator-=(const mint &m){n+=MOD-m.n; n=(n<MOD)?n:n-MOD; return *this;}

    mint& operator*=(const mint &m){n=n*m.n%MOD; return *this;}

    mint& operator/=(const mint &m){return *this*=m.inv();}

    mint& operator++(){return *this+=1;}

    mint& operator--(){return *this-=1;}



    mint operator+(const mint &m) const {return mint(*this)+=m;}

    mint operator-(const mint &m) const {return mint(*this)-=m;}

    mint operator*(const mint &m) const {return mint(*this)*=m;}

    mint operator/(const mint &m) const {return mint(*this)/=m;}

    mint operator++(int){mint t(*this); *this+=1; return t;}

    mint operator--(int){mint t(*this); *this-=1; return t;}



    bool operator==(const mint &m) const {return n==m.n;}

    bool operator!=(const mint &m) const {return n!=m.n;}

    mint operator-() const {return mint(MOD-n);}



    mint pow(value_type b) const {

        mint ret(1), m(*this);

        while(b){

            if (b & 1) ret*=m;

            m*=m;

            b>>=1;

        }

        return ret;

    }



    mint inv() const {return pow(MOD-2);}

};



//-------------------------------------------------



int main(void)

{

    cin.tie(0);

    ios::sync_with_stdio(false);

    ll n,k; cin>>n>>k;

    mint ans=mint(k-n-2)*(2*k*k-k*(n+2)-n*n-n-6)/6;

    cout<<ans<<"\n";

    return 0;

}


// Fastest known solution for this problem: