#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define inf 1e18
#define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define pb push_back
#define ff first
#define ss second
#define vll vector<ll>
#define pii pair<ll,ll>
#define sz(v) (v).size()
#define srt(v) sort(v.begin(),v.end())
#define ull unsigned long long
#define tell(a) cout<<a<<" "
#define el cout<<endl
#define rev(v) reverse(v.begin(),v.end())
#define rep(i,a,n) for(int i=a;i<n;i++)
#define M 1000000007
ll power(ll x, ll y, ll p){ll res = 1;x = x % p;while (y > 0){   if (y & 1)res = (res*x) % p;y = y>>1;
x = (x*x) % p;}return res;}

int main()
{
	IOS;
	ll n,k;
	cin>>n>>k;
	ll ans=0;
	for(ll i=k;i<=n+1;i++)
	{
		ans+=(n*i-(i)*(i-1)+1)%M;
		ans%=M;
	}
	cout<<ans;

}
