#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <cmath>
#include <queue>
#include <map>
#include <unordered_map>
#include <set>
#include <functional>
#include <bitset>
#include <cassert>
using namespace std;
using ll = long long;

int main() {
	ll n, k; cin >> n >> k;
	ll s = n*(n + 1) / 2;
	ll rev = s - (n - k)*(n - k + 1) / 2;
	ll mi = s - 2 * rev;
	cout << (s - mi)/2 + 1 << endl;
	return 0;
}