#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int inf = 1 << 30;
const ll INF = 1LL << 60;
const int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
#define rep(i, s, t) for (ll i = (ll)s; i < (ll)(t); i++)
#define rrep(i, s, t) for (ll i = (ll)(t) - 1; i >= (ll)(s); i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)

template <class T1, class T2>
bool chmin(T1& x, T2 y) { return x > y ? (x = y, true) : false; }
template <class T1, class T2>
bool chmax(T1& x, T2 y) { return x < y ? (x = y, true) : false; }

template <class T>
using min_heap = priority_queue<T, vector<T>, greater<T>>;
template <class T>
using max_heap = priority_queue<T>;

void solve() {
    ll X, N;
    cin >> X >> N;
    ll ok = 0, ng = 2 * (ll)sqrt(X) + 10;
    while (ng - ok > 1) {
        ll mid = (ok + ng) / 2;
        if ((__int128_t)mid * (mid + 1) / 2 <= abs(X)) ok = mid;
        else ng = mid;
    }
    if (N <= ok) {
        if (X > 0) X -= (__int128_t)N * (N + 1) / 2;
        else X += (__int128_t)N * (N + 1) / 2;
        cout << X << "\n";
    } else {
        ll M = N;
        if (X > 0) X -= (__int128_t)ok * (ok + 1) / 2;
        else X += (__int128_t)ok * (ok + 1) / 2;
        N -= ok;
        if (X > 0) {
            if (N % 2 == 0) X += N / 2;
            else X += N / 2 - M;
        } else {
            if (N % 2 == 0) X -= N / 2;
            else X -= N / 2 - M;
        }
        cout << X << "\n";
    }
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cout << fixed << setprecision(15);
    srand(time(NULL));

    int T;
    // cin >> T;
    T = 1;
    while (T--) solve();
}