#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include <map>
#include <fstream>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <assert.h>
#include <complex>
#include <omp.h>
using namespace std;
#define eps 0.000001
#define LONG_INF 10000000000000
#define GOLD 1.61803398874989484820458
#define seg_size 65536*4
#define REP(i,n) for(long long i = 0;i < n;++i)
unsigned long xor128() {
	static unsigned long x = time(NULL), y = 362436069, z = 521288629, w = 88675123;
	unsigned long t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
int main() {
	long long n, k;
	cin >> n >> k;
	long long bot = 0;
	long long top = n * (n + 1LL) / 2LL;
	n -= k;
	top -= (n) * (n + 1LL) / 2LL;
	long long ans = top;
	if (k % 2 == 1) {
		ans += 1LL;
	}
	else {
		ans += 1LL;
	}
	cout << ans << endl;
	return 0;
}