#include "bits/stdc++.h"
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define IOS std::cin.tie(0),std::ios::sync_with_stdio(false)

namespace idaten {

	using namespace std;
	using ll = int_fast64_t;
	using ull = uint_fast64_t;
	using P = std::pair<int64_t, int64_t>;
	template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
	template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
	template<class Type>struct is_vector : std::false_type {};
	template<class ValueType, class Alloc>struct is_vector<std::vector<ValueType, Alloc>> : std::true_type {};
	template <typename T> inline std::ostream& operator << (std::ostream& out, const std::vector<T>& v) {
		if (v.empty())return out;
		constexpr bool is_vector_v = is_vector<T>::value;
		if (is_vector_v)for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? "\n" : "");
		else for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? " " : "");
		return out;
	}
	inline void put() {}
	template<class T> inline void put(const T& first) { std::cout << first << "\n"; }
	template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first << " "; put(rest...); }
	inline void putn() {}
	template<class T, class... N> inline void putn(const T& first, const N& ... rest) { std::cout << first << "\n"; putn(rest...); }
	template<typename T, typename U>
	inline T pow(T x, U exp) {
		if (exp <= 0) {
			return 1;
		}
		if (exp % 2 == 0) {
			T d = pow(x, exp / 2);
			return d * d;
		} else {
			return (x * pow(x, exp - 1));
		}
	}

	template<typename T>
	inline T fact(int_fast32_t n) {
		static vector<T> table(1, 1);
		if (n >= (int)table.size()) {
			uint_fast32_t s = table.size();
			T t = s;
			for (int_fast32_t i = s; i < n + 1; ++i) {
				table.push_back(table.back() * t++);
			}
		}
		if (n < 0) return 1;
		else return table[n];
	}

	template<typename T>
	inline T invfact(int_fast32_t n) {
		static vector<T> invtable(1, 1);
		static int_fast64_t sz = 1;
		if (n >= sz) {
			int_fast64_t pre = sz;
			while (n >= sz) {
				sz *= 2;
			}
			invtable.resize(sz);
			invtable[sz - 1] = (T)1 / fact<T>(sz - 1);
			for (int_fast32_t i = sz - 1; i > pre; --i) {
				invtable[i - 1] = invtable[i] * i;
			}
		}
		if (n < 0) return 1;
		else return invtable[n];
	}

	template<typename T>
	inline T comb(uint_fast32_t n, uint_fast32_t m, bool closed = true) {//nCm
		if (n < m)return 0;
		else if (closed)return fact<T>(n) * invfact<T>(m) * invfact<T>(n - m);
		else return fact<T>(n) / fact<T>(m) / fact<T>(n - m);
	}

	template<int_fast64_t Mod>
	class ModInt {
		using lint = int_fast64_t;
	public:
		lint a;
		ModInt(lint val = 0) { if (val >= Mod) { val %= Mod; } else if (val < 0) { val %= Mod; val += Mod; }a = val; }
		ModInt operator-() { return ModInt(Mod - a); }//単項-演算子(-a)のオーバーロード
		ModInt operator=(const ModInt n) { a = n.a; return a; }
		ModInt operator+(const ModInt n) { if ((a + n.a) >= Mod) { return a + n.a - Mod; } else { return a + n.a; } }
		ModInt operator-(const ModInt n) { return a + (Mod - n.a); }
		ModInt operator*(const ModInt n) { return a * n.a; }
		ModInt operator/(const ModInt n) { return (*this) * pow(n, Mod - 2); }
		ModInt& operator+=(const ModInt n) { (*this) = (*this) + n; return *this; }
		ModInt& operator-=(const ModInt n) { (*this) = (*this) + (Mod - n.a); return *this; }
		ModInt& operator*=(const ModInt n) { (*this) = (*this) * n; return *this; }
		ModInt& operator/=(const ModInt n) { (*this) = (*this) / n; return *this; }
		ModInt operator++(int) { ModInt a = *this; (*this) += 1; return a; }//後置
		ModInt& operator++() { (*this) += 1; return *this; }//前置
		ModInt operator--(int) { ModInt a = *this; (*this) -= 1; return a; }//後置
		ModInt& operator--() { (*this) -= 1; return *this; }//前置
		ModInt inv() { return (ModInt)1 / (*this); }//逆数を返す関数
		bool operator<(const ModInt n) { return a < n.a; }
		bool operator<=(const ModInt n) { return a <= n.a; }
		bool operator>(const ModInt n) { return a > n.a; }
		bool operator>=(const ModInt n) { return a >= n.a; }
		bool operator==(const ModInt n) { return a == n.a; }
		bool operator!=(const ModInt n) { return a != n.a; }
		//下の関係演算子はpow関数で要請される
		bool operator<(const int n) { return a < n; }
		bool operator<=(const int n) { return a <= n; }
		bool operator>(const int n) { return a > n; }
		bool operator>=(const int n) { return a >= n; }
		bool operator==(const int n) { return a == n; }
		ModInt operator%(const int n) { return a % n; }
	};
	template<int_fast64_t Mod> inline ostream& operator <<(ostream& o, const ModInt<Mod>& t) { o << t.a; return o; }
	template<int_fast64_t Mod> inline istream& operator >>(istream& i, ModInt<Mod>& t) { i >> t.a; return i; }
	constexpr int_fast64_t mod = 1e9 + 7;
	//constexpr int_fast64_t mod = 998244353;
	using mi = ModInt<mod>;

	void solve() {
		IOS;
		ll n, k;
		cin >> n >> k;
		mi res;
		FOR(i, k, n + 2) {
			ll mi1 = i * (i - 1) / 2;
			ll ma1 = (n * 2 - i + 1) * i / 2;
			mi tmp = (ma1 - mi1 + 1) % mod;
			res += tmp;
		}
		put(res);
	}

} // namespace idaten

int main() {
	idaten::solve();
	return 0;
}


Measured memory_bytes: 3616