#include <bits/stdc++.h>
long long gcd(long long a, long long b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return (a * b) / gcd(a, b); }
const int MOD = 1e12 + 7;
const int MAX = 1e6 + 2;
const int INF = 0x3f3f3f3f;
bool IsPrime(long long x) {
  if (x < 2) {
    return false;
  }
  for (long long p = 2; p * p <= x; ++p)
    if (x % p == 0) return false;
  return true;
}
using namespace std;
int main() {
  long long n, k;
  cin >> n >> k;
  long long p = 0, q = 0;
  p = max(n - 2 * k, 0LL);
  q = n * (n - 1) / 2 - p * (p - 1) / 2;
  cout << q << endl;
  return 0;
}
