#pragma GCC optimize("O3")

#include "bits/stdc++.h"
#include <stdio.h>
#include "atcoder/all"
#include <boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;

using namespace std;
using namespace atcoder;

using ll = long long;
using ull = unsigned long long;
using mint = modint998244353;
using mint2 = modint1000000007;
const double eps = 1e-9;

#define OVERLOAD3(_1, _2, _3, call,...) call
#define REP0(n) for (ll i = 0; i < ll(n); ++i)
#define REP1(i, n) for (ll i = 0; i < ll(n); ++i)
#define REP2(i, a, b) for (ll i = ll(a); i < ll(b); ++i)
#define REP(...) OVERLOAD3(__VA_ARGS__, REP2, REP1, REP0)(__VA_ARGS__)
#define RREP0(n) for (ll i = ll(n) - 1; i >= 0; --i)
#define RREP1(i, n) for (ll i = ll(n) - 1; i >= 0; --i)
#define RREP2(i, a, b) for (ll i = ll(a) - 1; i >= b; --i)
#define RREP(...) OVERLOAD3(__VA_ARGS__, RREP2, RREP1, RREP0)(__VA_ARGS__)
#define REPE(i, c) for (const auto& i : c)
#define TCASE() ll _ttt; cin >> _ttt; while(_ttt--)

template<class... T> void COMMON_IN(T&... a) { (cin >> ... >> a); }
#define LI(...) ll __VA_ARGS__; COMMON_IN(__VA_ARGS__);

using vl = vector<ll>; using vvl = vector<vl>; using vvvl = vector<vvl>;
#define VLI(a, n) vector<ll> a; a.assign(n, 0); for(auto& x : a) cin >> x;
#define DLI(a, n) deque<ll> a; a.assign(n, 0); for(auto& x : a) cin >> x;
#define VSI(a, n) vector<string> a; a.assign(n, ""); for(auto& x : a) cin >> x;
#define VVLI(a, n, m) vector<vector<ll>> a(n, vector<ll>(m)); for(auto& x : a) for(auto& y : x) cin >> y;
using vd = vector<double>; using pl = pair<ll, ll>; using vpl = vector<pl>;

struct uv { ll u; ll v; ll c; };
#define VUVI(a, n) vector<uv> a; a.assign(n, {0, 0, 1}); for(auto& x : a) {cin >> x.u >> x.v; x.u--; x.v--;}
#define VUVCI(a, n) vector<uv> a; a.assign(n, {0, 0, 0}); for(auto& x : a) {cin >> x.u >> x.v >> x.c; x.u--; x.v--;}
vvl to_edge(const ll n, const vector<uv>& v) { vvl ret(n); for (auto& x : v) ret[x.u].push_back(x.v); return ret; }
vvl to_edge_d(const ll n, const vector<uv>& v) { vvl ret(n); for (auto& x : v) { ret[x.u].push_back(x.v); ret[x.v].push_back(x.u); } return ret; }

template <class T = long long> using pql = priority_queue<T>;
template <class T = long long> using pqg = priority_queue<T, vector<T>, greater<T>>;
using vm = vector<mint>; using vvm = vector<vm>;

ostream& operator<<(ostream& os, const mint& v) { os << v.val(); return os; }
void yn(bool f) { std::cout << (f ? "Yes" : "No") << "\n"; };
template<class T> void ov(const T& v) { for (auto it = v.begin(); it != v.end(); it++) { if (it != v.begin()) cout << " "; cout << *it; } };
template<> void ov(const vm& v) { for (auto it = v.begin(); it != v.end(); it++) { if (it != v.begin()) cout << " "; cout << it->val(); } };

const ll llhuge = 1LL << 61; //十分でかいが多少足しても溢れない数値
auto gmax(const auto& a, const auto& b) { return a > b ? a : b; };
auto gmin(const auto& a, const auto& b) { return a < b ? a : b; };
bool chmin(auto& a, const auto& b) { const auto olda = a; a = gmin(a, b); return olda != a; }
bool chmax(auto& a, const auto& b) { const auto olda = a; a = gmax(a, b); return olda != a; }
void sort(auto& v) { std::ranges::sort(v); };
void rev(auto& v) { std::ranges::reverse(v); };
template<class T> auto p_sum(const T& v) { T ret(v.size()); std::partial_sum(begin(v), end(v), ret.begin()); return ret; };
template<class T, class K = T::key_type, class V = T::mapped_type> [[nodiscard]] V myat(const T& mp, const K& key) { return mp.find(key) == mp.end() ? V() : mp.at(key); }
long long ceil(const long long a, const long long b) { return (a + b - 1) / b; }

template <class F>
cpp_int bs(cpp_int ng, cpp_int ok, F f) {
	while (abs(ok - ng) > 1) {
		cpp_int mid = (ok + ng) / 2;

		if (f(mid)) ok = mid;
		else ng = mid;
	}
	return ok;
}

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

	cpp_int x, n;
	cin >> x >> n;
	bool flip = (x < 0);
	x = abs(x);

	cpp_int all = n * (n + 1) / 2;
	if (x > all) {
		cpp_int ans = x - all;
		if (flip) ans = -ans;
		cout << ans << endl;
		return 0;
	}

	cpp_int nv = 1;
	if (x > 0) {
		cpp_int tn = bs(n, 0, [&](cpp_int t) {
			return t * (t + 1) / 2 <= abs(x);
		});
		n -= tn;
		nv = tn + 1;
		x -= tn * (tn + 1) / 2;
	}
	if (flip) x = -x;
	if (n % 2 == 1) {
		if (x <= 0) x += nv;
		else x -= nv;
		n--;
	}
	if (x > 0) cout << x + (n / 2) << endl;
	else cout << x - (n / 2) << endl;
}