#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  ll x, n;
  cin >> x >> n;
  auto s = [](ll i) -> ll { return (i + 1) * i / 2; };
  ll i;
  {
    ll ok = 0, ng = 2e9;
    while (ok + 1 < ng) {
      ll m = (ok + ng) / 2;
      if (s(m) <= abs(x)) {
        ok = m;
      } else {
        ng = m;
      }
    }
    i = min(ok, n);
  }
  if (x <= 0) {
    x += s(i);
  } else {
    x -= s(i);
  }
  if (i == n) {
    cout << x << '\n';
    return;
  }
  if (x <= 0) {
    i += 1;
    x += i;
  }
  ll ans;
  if ((n - i) % 2 == 0) {
    ans = x + (n - i) / 2;
  } else {
    i += 1;
    x -= i;
    ans = x - (n - i) / 2;
  }
  cout << ans << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}