#include <bits/stdc++.h>
#define REP(i, n) for(int i = 0; i < n; i++)
#define REP1(i,n) for(int i = 1; i < n+1 ;i++)
#define REPR(i, n) for(int i = n; i >= 0; i--)
#define FOR(i, m, n) for(int i = m; i < n; i++)
#define INF 2e9
#define ALL(v) v.begin(), v.end()
#define SZ(x) ((int)(x).size())
#define ARRAY_LENGTH(array) (sizeof(array) / sizeof(array[0]))
using namespace std;
typedef long long ll;
using p = pair<int, int>;
using P = pair<ll, ll>;
using V = vector<int>;
using VV = vector<vector<int>>;
using VVV = vector<vector<vector<int>>>;
using VL = vector<ll>;
using VVL = vector<vector<ll>>;
using VVVL = vector<vector<vector<ll>>>;
using Graph = VV;
const int MAX = 510000;
const int MOD = 1000000007;

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

int main(){
    COMinit();
    ios::sync_with_stdio(false); cin.tie(0);
    int n,k;
    cin >> n >> k;
    ll ans = 0;
    FOR(i,k,n+2){
        if(k == n+1) ans++;
        else{
            ans+=i*(2*n-i+1)/2 - i*(i-1)/2;
        }
    }
    cout << ans << endl;


}
 