#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)
const int mod=1000000007;

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