// #include <ext/pb_ds/assoc_container.hpp> 
//#include <ext/pb_ds/tree_policy.hpp>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <cstring>
#include <vector>
#include <deque>
#include <queue>
#include <set>
#include <map>
#include <valarray>
#include <iterator>
#include <functional>
#include <limits>
#include <algorithm>
#include <numeric>
#include <cmath>
#include <cassert>
#include <unordered_map>
#include <unordered_set>
#include <stack>
using namespace std;
#define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define trace(x) cerr << #x << ": " << x << " " << endl;
 
typedef int64_t ll;
 
#define endl '\n'
#define int ll
ll mod=1e9+7;
ll mod1=1e9+5;
ll power(ll a,ll b)
{
    if(b==0) return 1;
    else if(b%2==0)
        return power(((((a)%mod)*((a)%mod))%mod),b/2)%mod;
    else return (((a)%mod)*(power(((((a)%mod)*((a)%mod))%mod),b/2)%mod))%mod;
}
inline ll inverse(ll a,ll md) {
  a %= md;
  if (a < 0) a += md;
  ll b = md, u = 0, v = 1;
  while (a) {
    ll t = b / a;
    b -= t * a; swap(a, b);
    u -= t * v; swap(u, v);
  }
  assert(b == 1);
  if (u < 0) u += md;
  return u;
}
  
  
 //using namespace __gnu_pbds;
 //#define ordered_set tree<pair<int,int>, null_type,less<pair<int,int>>, rb_tree_tag,tree_order_statistics_node_update>
//find_by_order(k)  returns iterator to kth element starting from 0;
//order_of_key(k) returns count of elements strictly smaller than k;
//erase,insert same as normal set
// mt19937 mrand(chrono::high_resolution_clock::now().time_since_epoch().count()); for randomized solution
const int ce=1e9+7;
ll fast_mod(ll input)
{
    return input < ce ? input : input%ce;
}
#define pi 3.14159
int32_t main()
{
    IOS
 
	int n,k;
	cin>>n>>k;
	int a[n+2];
	for(int i=1;i<=n+1;i++)
		a[i]=i-1;
	int sum[n+2];
	sum[0]=0;
	for(int i=1;i<=n+1;i++)
	{
		sum[i]=sum[i-1]+a[i];
	}
	int ans=0;
	for(int i=k;i<=n+1;i++)
	{
		ans+=sum[n+1]-sum[n+1-i]-sum[i]+1;
		ans%=mod;
	}
	cout<<ans<<endl;
}       