#include <bits/stdc++.h>
void answer(unsigned long long v) { std::cout << v << '\n'; }
void solve(unsigned n, unsigned k) {
  const auto s = n * (n - 1ull) / 2;
  if (k > n / 2) return answer(s);
  const auto m = n - 2 * k;
  const auto d = m * (m - 1ull) / 2;
  answer(s - d);
}
int main() {
  unsigned n, k;
  std::cin >> n >> k;
  solve(n, k);
  return 0;
}
