#include <limits>
#include <new>
#include <typeinfo>
#include <exception>
#include <initializer_list>
#include <stdexcept>
#include <system_error>
#include <utility>
#include <bitset>
#include <ratio>
#include <tuple>
#include <optional>
#include <variant>
#include <any>
#include <type_traits>
#include <functional>
#include <memory>
#include <scoped_allocator>
#include <chrono>
#include <typeindex>
#include <string>
#include <string_view>
#include <locale>
#include <array>
#include <deque>
#include <forward_list>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <iterator>
#include <algorithm>
#include <complex>
#include <random>
#include <valarray>
#include <numeric>
#include <iosfwd>
#include <iostream>
#include <ios>
#include <streambuf>
#include <istream>
#include <ostream>
#include <iomanip>
#include <sstream>
#include <fstream>
#include <regex>
#include <atomic>
#include <thread>
#include <mutex>
#include <shared_mutex>
#include <condition_variable>
#include <future>
#include <cassert>
#include <cctype>
#include <cerrno>
#include <cfenv>
#include <cfloat>
#include <cinttypes>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <cuchar>
#include <cwchar>
#include <cwctype>

#define For(i, a, b) for(int (i)=(int)(a); (i)<(int)(b); ++(i))
#define rFor(i, a, b) for(int (i)=(int)(a)-1; (i)>=(int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;
template<class T> bool chmax(T &a, const T &b){if(a<b){a=b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b){if(a>b){a=b; return true;} return false;}
template<class T> T div_floor(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>=0 ? a/b : (a+1)/b-1;
}
template<class T> T div_ceil(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>0 ? (a-1)/b+1 : a/b;
}

constexpr lint mod = 1e9+7;
constexpr lint INF = mod * mod;
constexpr int MAX = 200010;

template<int_fast64_t MOD> struct modint{
    using i64=int_fast64_t;
    i64 a;
    modint(const i64 a_=0): a(a_){
        if(a>MOD) a%=MOD;
        else if(a<0) (a%=MOD)+=MOD;
    }
    modint inv(){
        i64 t=1, n=MOD-2, x=a;
        while(n){
            if(n&1) (t*=x)%=MOD;
            (x*=x)%=MOD;
            n>>=1;
        }
        modint ret(t);
        return ret;
    }
    bool operator==(const modint x) const{return a==x.a;}
    bool operator!=(const modint x) const{return a!=x.a;}
    modint operator+(const modint x) const{
        return modint(*this)+=x;
    }
    modint operator-(const modint x) const{
        return modint(*this)-=x;
    }
    modint operator*(const modint x) const{
        return modint(*this)*=x;
    }
    modint operator/(const modint x) const{
        return modint(*this)/=x;
    }
    modint operator^(const lint x) const{
        return modint(*this)^=x;
    }
    modint &operator+=(const modint &x){
        a+=x.a;
        if(a>=MOD) a-=MOD;
        return *this;
    }
    modint &operator-=(const modint &x){
        a-=x.a;
        if(a<0) a+=MOD;
        return *this;
    }
    modint &operator*=(const modint &x){
        (a*=x.a)%=MOD;
        return *this;
    }
    modint &operator/=(modint x){
        (a*=x.inv().a)%=MOD;
        return *this;
    }
    modint &operator^=(lint n){
        i64 ret=1;
        while(n){
            if(n&1) (ret*=a)%=MOD;
            (a*=a)%=MOD;
            n>>=1;
        }
        a=ret;
        return *this;
    }
    modint operator-() const{
        return modint(0)-*this;
    }
    modint &operator++(){
        return *this+=1;
    }
    modint &operator--(){
        return *this-=1;
    }
    bool operator<(const modint x) const{
        return a<x.a;
    }
};

using mint=modint<1000000007>;

vector<mint> fact;
vector<mint> revfact;

void setfact(int n){
    fact.resize(n+1); revfact.resize(n+1);
    fact[0] = 1;
    rep(i, n) fact[i+1] = fact[i] * mint(i+1);

    revfact[n] = fact[n].inv();
    for(int i=n-1; i>=0; i--) revfact[i] = revfact[i+1] * mint(i+1);
}

mint getC(int n, int r){
    if(n<r) return 0;
    return fact[n] * revfact[r] * revfact[n-r];
}

mint f(int i){
    return mint(i) * mint(i+1) / mint(2);
}

int main(){
    int n, K;
    scanf("%d%d", &n, &K);
    mint ans = 0;
    For(i, K, n+2){
        ans += f(n) - f(n-i) - f(i-1) + 1;
    }
    printf("%lld\n", ans.a);
}

Measured memory_bytes: 3820