#include <bits/stdc++.h>
#include <stdlib.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;
typedef pair<ll,ll> P;
typedef priority_queue<P,vector<P>,greater<P>> P_queue;

#define REP(i,a,b) for(int i=(int)a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define mp make_pair
#define ALL(a) a.begin(),a.end()
#define SORT(a) sort(ALL(a))
#define U_ERASE(V) V.erase(unique(ALL(V)), V.end());

const ll MOD=998244353;
const ll mod=1000000007;
const ll INF=1e15;
vec dx={1,0,-1,0};
vec dy={0,1,0,-1};

int main(){
    ll N,K; cin>>N>>K;
    ll ans=0;
    REP(i,K,N+2){
        ans+=(i*(N-i+1));
        ans++;
        ans%=mod;
    }
    cout<<ans<<endl;
}