#if __INCLUDE_LEVEL__ == 0

#include __BASE_FILE__

void Solve() {
  int64_t x0, n;
  IN(x0, n);

  if (x0 > 0) {
    // x0 以上
    int64_t ng = 0;
    int64_t ok = 1.5e9;
    while (ng + 1 < ok) {
      int64_t mid = midpoint(ng, ok);
      (mid * (mid + 1) / 2 >= x0 ? ok : ng) = mid;
    }

    if (n <= ok) {
      x0 -= n * (n + 1) / 2;
      OUT(x0);
      return;
    }

    x0 -= ok * (ok + 1) / 2;
    assert(x0 <= 0);

    // ok+1, ..., n
    if ((n - ok) % 2 == 0) {
      x0 -= (n - ok) / 2;
    } else {
      x0 -= (n - ok - 1) / 2;
      x0 += n;
    }
    OUT(x0);

  } else {
    // -x0 より大
    int64_t ng = 0;
    int64_t ok = 1.5e9;
    while (ng + 1 < ok) {
      int64_t mid = midpoint(ng, ok);
      (mid * (mid + 1) / 2 > -x0 ? ok : ng) = mid;
    }

    if (n <= ok) {
      x0 += n * (n + 1) / 2;
      OUT(x0);
      return;
    }

    x0 += ok * (ok + 1) / 2;
    assert(x0 > 0);

    // ok+1, ..., n
    if ((n - ok) % 2 == 0) {
      x0 += (n - ok) / 2;
    } else {
      x0 += (n - ok - 1) / 2;
      x0 -= n;
    }
    OUT(x0);
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  Solve();
}

#elif __INCLUDE_LEVEL__ == 1

#include <bits/stdc++.h>

template <class T> concept MyRange = std::ranges::range<T> && !std::convertible_to<T, std::string_view>;
template <class T> concept MyTuple = std::__is_tuple_like<T>::value && !MyRange<T>;

namespace std {

istream& operator>>(istream& is, MyRange auto&& r) {
  for (auto&& e : r) is >> e;
  return is;
}
istream& operator>>(istream& is, MyTuple auto&& t) {
  apply([&](auto&... xs) { (is >> ... >> xs); }, t);
  return is;
}

ostream& operator<<(ostream& os, MyRange auto&& r) {
  auto sep = "";
  for (auto&& e : r) os << exchange(sep, " ") << e;
  return os;
}
ostream& operator<<(ostream& os, MyTuple auto&& t) {
  auto sep = "";
  apply([&](auto&... xs) { ((os << exchange(sep, " ") << xs), ...); }, t);
  return os;
}

}  // namespace std

using namespace std;

#define IN(...) (cin >> forward_as_tuple(__VA_ARGS__))
#define OUT(...) (cout << forward_as_tuple(__VA_ARGS__) << '\n')

#endif  // __INCLUDE_LEVEL__ == 1