#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:268435456")
using namespace std;
template <typename T>
inline T abs(T a) {
  return ((a < 0) ? -a : a);
}
template <typename T>
inline T sqr(T a) {
  return a * a;
}
template <class T>
T gcd(T a, T b) {
  return a ? gcd(b % a, a) : b;
}
template <class T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
template <class T>
T sign(T a) {
  return a > 0 ? 1 : (a < 0 ? -1 : 0);
}
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
const int dxK[] = {-1, -1, 0, 1, 1, 1, 0, -1};
const int dyK[] = {0, 1, 1, 1, 0, -1, -1, -1};
const int dxKn[] = {-2, -1, 1, 2, 2, 1, -1, -2};
const int dyKn[] = {1, 2, 2, 1, -1, -2, -2, -1};
const int N = int(1e6) + 9;
const int M = int(1e3) + 9;
const int LOGN = 21;
const int SQN = 350;
const int MOD = int(1e9) + 7;
const int INF = 1e9 + 100;
const long long INF64 = 2e18;
const long double PI = 3.1415926535897932384626433832795;
const long double EPS = 1e-9;
int a[N];
int f[N];
int sum(int pos) {
  int sum = 0;
  for (; pos >= 0; pos = (pos & (pos + 1)) - 1) sum += f[pos];
  return sum;
}
void upd(int pos) {
  for (; pos < N; pos |= pos + 1) ++f[pos];
}
void solve() {
  int n, k;
  cin >> n >> k;
  long long res = 0, d = n - 1;
  for (int i = 0; i < (int)(n); ++i) a[i] = i;
  for (int l = 0, r = n - 1; l < r && k > 0; ++l, --r, --k) swap(a[l], a[r]);
  for (int i = int(n) - 1; i >= 0; --i) {
    int pos = a[i];
    --pos;
    res += sum(pos);
    upd(pos + 1);
  }
  cout << res;
}
int main() {
  srand(time(NULL));
  srand(time(NULL));
  cout << setprecision(10) << fixed;
  cerr << setprecision(10) << fixed;
  solve();
  return 0;
}
