#include <bits/stdc++.h>

using namespace std;

#define rep(i, n) for (int i = 0; i < (n); ++i)

using ll = long long;
using pint = pair<int, int>;
using mint = map<int, int>;

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

const char sp = ' ';
const char cmm = ',';
const int MOD = 1e9+7;
const int INF = 1e9;
const ll LINF = 1e18;

ll mod(ll a, ll b){return (a%b+b)%b;}
ll gcd(ll a, ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b){return a*b/gcd(a,b);}
void Yes(){cout << "Yes" << endl;}
void No(){cout << "No" << endl;}
void Judge(bool b){b?Yes():No();}
void YES(){cout << "YES" << endl;}
void NO(){cout << "NO" << endl;}
void JUDGE(bool b){b?YES():NO();}
ll powMod(ll b, ll e, ll m){ll r=1;while(e>0){if(e&1)r=(r%m)*(b%m)%m;b=(b%m)*(b%m)%m;e>>=1;}return r;}
double distance(ll x1, ll y1, ll x2, ll y2){return sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));}

template<typename T>
void ppp(T n){cout << n << endl;}
template<typename T1, typename T2> ostream& operator<<(ostream& s, const pair<T1, T2>& p) {return s << "(" << p.first << ", " << p.second << ")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& v) {
	int len = v.size();
    s << '[';
	for (int i = 0; i < len; ++i) {
		s << v[i]; if (i < len-1) s << ", ";
	}
    s << ']';
	return s;
}

const int MAX = 510000;

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

void combinit(){
    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;
    }
}


ll com(int n, int k){
    if(n < k) return 0;
    if(n < 0 or k < 0) return 0;
    return fac[n] * (finv[k] * finv[n-k] % MOD) % MOD;
}
int main(){

    cin.tie(0);
    ios::sync_with_stdio(false);

	ll n, k;
	cin >> n >> k;

	ll ans = k*(2*n-k+1)/2+1;
	ppp(ans);

    return 0;
}