#include <bits/stdc++.h>
#include <cmath>
#include <map>
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define been(ix) (ix).begin(),(ix).end()
using namespace std;
typedef long long ll; 
typedef vector<int> vi;
typedef vector<long long> vl;
const ll INF = 1e18;
typedef pair<int,int> P;
#define foreach(ix,i) for(auto& (ix) : (i))
typedef long double ld;
const int mod = 1000000007;
//const int mod = 998244353;
struct mint {
  ll x;
  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;
  }
  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;}
};
mint choose(int n,int a){
  mint x = 1,y=1;
  rep(i,a){
    x*= n-i;
    y*= i+1;
  }
  return x/y;
}
int main(){
  ll n,k;
  cin>>n>>k;
  vector<ll> sum(n+2,0);
  sum[0]=0;
  rep(i,n+1){
    if(i==0)continue;
    sum[i]=sum[i-1]+i;
  }
  ll ans =0;
  for(int i=k;i<=n+1;i++){
    if(i==n+1)ans++;
    else{
    ans+=(sum[n]-sum[n-i])-sum[i-1]+1;
  }
  ans%=mod;
  }
  cout<<ans<<endl;
}