#include <bits/stdc++.h>
using namespace std;

typedef unsigned long ul;
typedef unsigned long long ull;
typedef long long ll;
typedef vector<ll> vint;
typedef vector< vector<ll> > vvint;
typedef vector< vector< vector<ll> > > vvvint;
typedef vector<string> vstring;
typedef vector< vector<string> > vvstring;
typedef vector<char> vchar;
typedef vector< vector<char> > vvchar;
typedef vector<long double> vdouble;
typedef vector< vector<long double> > vvdouble;
typedef vector< vector< vector<long double> > > vvvdouble;
typedef pair<ll,ll> pint;
typedef vector<pint> vpint;
typedef vector<bool> vbool;

#define rep(i,n) for(ll i=0;i<n;i++)
#define repf(i,f,n) for(ll i=f;i<n;i++)
#define repr(i,n) for(ll i=n-1;i>=0;i--)
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define ALL(obj) (obj).begin(), (obj).end()
// #define LLONG_MAX 9223372036854775806
#define MOD 1000000007
const double PI=3.14159265358979323846;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
template<typename T> T Ceil(T a, T b){return (a+b-1)/b;}

int dy[]={0, 0, 1, -1, 1, -1, -1, 1};
int dx[]={1, -1, 0, 0, 1, 1, -1, -1};

void printv(vint &v){
    for(auto e:v) cout<<e<<" ";
        cout<<endl;
    }
template< int mod >
struct ModInt {
int x;

ModInt() : x(0) {}

ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

ModInt &operator+=(const ModInt &p) {
if((x += p.x) >= mod) x -= mod;
return *this;
}

ModInt &operator-=(const ModInt &p) {
if((x += mod - p.x) >= mod) x -= mod;
return *this;
}

ModInt &operator*=(const ModInt &p) {
x = (int) (1LL * x * p.x % mod);
return *this;
}

ModInt &operator/=(const ModInt &p) {
*this *= p.inverse();
return *this;
}

ModInt operator-() const { return ModInt(-x); }

ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

bool operator==(const ModInt &p) const { return x == p.x; }

bool operator!=(const ModInt &p) const { return x != p.x; }

ModInt inverse() const {
int a = x, b = mod, u = 1, v = 0, t;
while(b > 0) {
t = a / b;
swap(a -= t * b, b);
swap(u -= t * v, v);
}
return ModInt(u);
}

ModInt pow(int64_t n) const {
ModInt ret(1), mul(x);
while(n > 0) {
if(n & 1) ret *= mul;
mul *= mul;
n >>= 1;
}
return ret;
}

friend ostream &operator<<(ostream &os, const ModInt &p) {
return os << p.x;
}

friend istream &operator>>(istream &is, ModInt &a) {
int64_t t;
is >> t;
a = ModInt< mod >(t);
return (is);
}

static int get_mod() { return mod; }
};

using modint = ModInt< (int)(1e9+7) >;

template< typename T >
struct Combination {
vector< T > _fact, _rfact, _inv;

Combination(int sz) : _fact(sz + 1), _rfact(sz + 1), _inv(sz + 1) {
_fact[0] = _rfact[sz] = _inv[0] = 1;
for(int i = 1; i <= sz; i++) _fact[i] = _fact[i - 1] * i;
_rfact[sz] /= _fact[sz];
for(int i = sz - 1; i >= 0; i--) _rfact[i] = _rfact[i + 1] * (i + 1);
for(int i = 1; i <= sz; i++) _inv[i] = _rfact[i] * _fact[i - 1];
}

inline T fact(int k) const { return _fact[k]; }

inline T rfact(int k) const { return _rfact[k]; }

inline T inv(int k) const { return _inv[k]; }

T P(int n, int r) const {
if(r < 0 || n < r) return 0;
return fact(n) * rfact(n - r);
}

T C(int p, int q) const {
if(q < 0 || p < q) return 0;
return fact(p) * rfact(q) * rfact(p - q);
}

T H(int n, int r) const {
if(n < 0 || r < 0) return (0);
return r == 0 ? 1 : C(n + r - 1, r);
}
};
int main() {
    cout<<fixed<<setprecision(10);

    ll n,k; cin>>n>>k;
    modint ans = 1;

    vint rui(n+2,0);
    rep(i,n+1) rui[i+1] = rui[i] + i;

    repf(i,k,n+1){
        ll minval, maxval;
        minval = rui[i];
        maxval = rui[n+1] - rui[n+1-i];
        ans += maxval - minval + 1;
    }
    cout<<ans<<endl;

    return 0;

}

Measured memory_bytes: 4756