#include <bits/stdc++.h>

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  long long x, n; std::cin >> x >> n;
  if (x > 0) {
    long long ok = 0, ng = 4e9;
    while (ng - ok > 1) {
      long long mid = (ok + ng) / 2;
      (mid * (mid + 1) / 2 <= x ? ok : ng) = mid;
    }
    if (n < ok) {
      std::cout << x - n * (n + 1) / 2 << '\n';
      return 0;
    }
    x -= ok * (ok + 1) / 2;
    if ((n - (ok + 1)) % 2 == 0) {
      x += (n - (ok + 1)) / 2;
      x -= n;
    } else {
      x += (n - (ok + 1) + 1) / 2;
    }
    std::cout << x << '\n';
  } else {
    long long ok = 0, ng = 4e9;
    while (ng - ok > 1) {
      long long mid = (ok + ng) / 2;
      (mid * (mid + 1) / 2 <= -x ? ok : ng) = mid;
    }
    if (n < ok) {
      std::cout << x + n * (n + 1) / 2 << '\n';
      return 0;
    }
    x += ok * (ok + 1) / 2;
    if ((n - (ok + 1)) % 2 == 0) {
      x -= (n - (ok + 1)) / 2;
      x += n;
    } else {
      x -= (n - (ok + 1) + 1) / 2;
    }
    std::cout << x << '\n';
  }
}