#include <algorithm>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <deque>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#define FOR(i,k,n) for(int(i)=(k);(i)<(n);++(i))
#define rep(i,n) FOR(i,0,n)
#define all(v) begin(v),end(v)
#define debug(x) std::cerr<<#x<<": "<<x<<"\n"
#define debug2(x,y) std::cerr<<#x<<": "<<x<<", "<<#y<<": "<<y<<"\n"
#define debug3(x,y,z) std::cerr<<#x<<": "<<x<<", "<<#y<<": "<<y<<", "<<#z<<": "<<z<<"\n"

using ll=long long;
using vi=std::vector<int>;
using vvi=std::vector<vi>;
using vll=std::vector<ll>;
using vvll=std::vector<vll>;
template<typename T> using vvec=std::vector<std::vector<T>>;
template<typename T>
auto make_v(size_t sz){return std::vector<T>(sz);}
template<typename T,typename... Ts>
auto make_v(size_t sz,Ts...ts){return std::vector<decltype(make_v<T>(ts...))>(sz,make_v<T>(ts...));}
template<typename T>
void fill_v(T&var,const T&x){var=x;}
template<typename V,typename T>
void fill_v(V&v,const T&x){for(auto&& w:v){fill_v(w,x);}}

template<typename T> std::ostream& operator<<(std::ostream&s,const std::vector<T>&v){
  int sz=v.size();s<<"\n";rep(i,sz){s<<v[i];if(i<sz-1){s<<"\t";}}s<<"\n";return s;}
template<typename T> std::ostream& operator<<(std::ostream&s,const std::vector<std::vector<T>>&v){
  for(auto&& w:v){s<<w;}return s;}
template<typename T> std::ostream& operator<<(std::ostream&s,const std::deque<T>&v){
  int sz=v.size();s<<"\n";rep(i,sz){s<<v[i];if(i<sz-1){s<<"\t";}}s<<"\n";return s;}
template<typename T> std::ostream& operator<<(std::ostream&s,const std::deque<std::deque<T>>&v){
  for(auto&& w:v){s<<w;}return s;}
template<typename T> std::ostream& operator<<(std::ostream&s, const std::set<T>&v){
  s<<"\n";for(auto&& elm:v){s<<elm<<"\t";}s<<"\n";return s;}

inline void scan(int&a){scanf("%d",&a);}
inline void scan(ll&a){scanf("%lld",&a);}
inline void scan(char&a){scanf(" %c",&a);}
inline void scan(double&a){scanf("%lf",&a);}
template<typename T>
inline void scan(std::vector<T>&v){for(auto&& sv:v){scan(sv);}}
template<typename First,typename...Args>
inline void scan(First&f,Args&...args){scan(f);scan(args...);}
inline void scan(std::string&s){char BUF[3000000];scanf(" %s",BUF);s=std::string(BUF);}
inline void print(int a){printf("%d\n",a);}
inline void print(ll a){printf("%lld\n",a);}
inline void print(double a){printf("%.12f\n",a);}
inline void print(std::string s){std::cout<<s<<"\n";}

#include <sstream>
#include <iomanip>
using namespace std;

vll pre_listing() {
  vll all_lun;
  all_lun.reserve(110000);
  vll dp(10);
  iota(all(dp), 0);
  rep (i, 9) {
    vll dp2;
    dp2.reserve(dp.size() * 3);
    for (ll num : dp) {
      // https://stackoverflow.com/questions/225362/convert-a-number-to-a-string-with-specified-length-in-c
      std::stringstream ss;
      ss << std::setw(i+1) << std::setfill('0') << num;
      std::string num_string = ss.str();

      //auto num_string = to_string(num);
      if (num_string[0] > '1') {
        all_lun.push_back(num);
      }
      for (char c = num_string[0] - 1; c <= num_string[0] + 1; ++c) {
        if (c < '0' || '9' < c) {
          continue;
        }
        dp2.push_back(stoll(c + num_string));
      }
    }
    swap(dp, dp2);
  }
  set<int> all_lun_s;
  vll all_lun_tmp;
  for (ll num : all_lun) {
    if (0 < num && num <= 3234566667) {
      all_lun_tmp.push_back(num);
    }
  }
  for (ll num : dp) {
    if (0 < num && num <= 3234566667) {
      all_lun.push_back(num);
    }
  }
  sort(all(all_lun));
  return all_lun;
}

int mod = 1000000007;
void solve() {
  int n, k;
  scan(n, k);
  vi a(n+1);
  iota(begin(a), end(a), 0);
  vll acc(n+2, 0);
  rep (i, n+1) {
    acc[i+1] = acc[i] + a[i];
  }
  ll ans = 0;
  FOR (i, k, n+2) {
    ll mi = acc[i] - acc[0];
    ll ma = acc[n+1] - acc[n+1-i];
    ans = (ans + ma - mi + 1) % mod;
  }
  print(ans);
}

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


Measured memory_bytes: 5268