#include <bits/stdc++.h>
#define repr(i,a,b) for(int i=a;i<b;i++)
#define rep(i,n) for(int i=0;i<n;i++)
typedef long long int ll;
using namespace std;
ll ans;
ll f(ll a, ll d, ll n) {
	return (a * 2 + d * (n - 1)) * n / 2;
}
int main(void) {
	ios::sync_with_stdio(false);
	ll n, k; cin >> n >> k;
	cout << 1 + f(n, -1,k) << endl;
	return 0;
}