#include <bits/stdc++.h>
using namespace std;

//repetition
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i, n) for(int i = 0; i < (int)(n); i++)

//container util
#define all(x) (x).begin(),(x).end()

//typedef
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VLL;
typedef vector<VLL> VVLL;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;

// 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;
	if (k == 0) return 1;
	return n * COM(n - 1, k - 1) / k;
}

long long Pow(int x, int n){
  if(n == 0) return 1;
  if(n % 2 == 0) {
    long long sqrtX = Pow(x,n/2);
    return sqrtX * sqrtX ;
  }else{
    return x * Pow(x,n-1);
  }
}

//conversion
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}


int main(){
    ll n,k;
    cin >> n >> k;
    ll ans = 0;
    ans = 1;

    cout << 1LL + k*(n+n-k+1)/2LL << endl;

    return 0;
}