#include <bits/stdc++.h>
#define rep(i,n) for(long long i=0; i<n; i++)
#define Rep(i,n) for(long long i=1; i<n; i++)
#define ll long long
#include <math.h>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <queue>
#include <set>
#include <vector>


using namespace std;
#define PI acos(-1)
using P =pair<ll,ll>;

ll ketasu(ll a){
   ll num=1;
   while(a/10){
       num++;
       a/=10;
   }
   return num;
}

ll gcd(ll a,ll b){return b ? gcd(b,a%b) :a;}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}

ll kosuu(ll a){
    ll sum=0;
    for(ll i=1;i*i<=a;i++){
        if(a%i==0){
            if(a!=1&&i*i!=a){
            sum+=2;
            }else{
             sum++;   
            }
        }
    }
    return sum;
}






ll di[]={1,0,-1,0};
ll dj[]={0,-1,0,1};

struct UnionFind {
    vector<int>d;
    UnionFind(int n=0):d(n,-1){}
    int find(int x){
        if((d[x])<0)return x;
        return d[x]=find(d[x]);
    }
    bool unite(int x,int y){
        x =find(x);y=find(y);
        if(x==y)return false;
        if(d[x]>d[y])swap(x,y);
        d[x]+=d[y];
        d[y]=x;
        return true;
    }
    bool same(int x,int y){return find(x)==find(y);};
    int size(int x){return -d[find(x)];};
};




// 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;
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, mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}

mint f(int n) {
    if(n==0)return 1;
    mint x=f(2/n);
    x*=x;
    if(n%2==1)x*=2;
    return x;
}

mint choose(int n,int a){
    mint x =1,y=1;
    rep(i,a){
      x*=n-i;
      y*=a+i;
    }
    return x/y;
}

vector<ll>to[1000000];
const ll inf=10000000007;

vector<ll>a,b,c,d;
ll n,m,q;
ll ans=0;

void dfs(vector<ll> v){
    if(v.size()==n+1){
        ll sum=0;
        rep(i,q){
          if(v[b[i]-1]-v[a[i]-1]==c[i])sum+=d[i];
        }
        ans=max(ans,sum);
        return;
    }
    v.push_back(v.back());
    dfs(v);
    while(v.back()!=m){
      v.back()++;
      dfs(v);
    }
}

int main()
{ 
  ll n,k;
  cin>>n>>k;
  ll m=1000000007;
  ll sum=0;
  for(ll i=k;i<=n+1;i++){
      ll e=(n*i-i*i+i+1)%m;
      sum+=e;
      sum%=m;
  }
  cout<<sum<<endl;
}
 
 




Measured memory_bytes: 27064