#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>
#include <cmath>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<ll> vi;

#define forn(i, n) for (int (i) = 0; (i) != (n); (i)++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define fi first
#define se second

#ifdef LOCAL
#define dbg(x) cerr << __LINE__ << " " << #x << " " << x << endl
#define ln cerr << __LINE__ << endl
#else
#define dbg(x) void(0)
#define ln void(0)
#endif // LOCAL

const int N = 15;
const int M = 500;
const int MOD = 1e9 + 7;
const int alpha = 26;

int n, k;
ll ans = 0;

signed main()
{
    #ifdef ONLINE_JUDGE
        ios_base::sync_with_stdio(false);
        cin.tie(0);
        cout.tie(0);
    #endif // ONLINE_JUDGE
    cin >> n >> k;
    for (int ch = k; ch <= n + 1; ch++)
    {
        ll mn = ch * (ch - 1) / 2;
        ll mx = (n + n - ch + 1) * ch / 2;
        ans = (ans + mx - mn + 1) % MOD;
    }
    cout << ans;
}
