#include <bits/stdc++.h>
using namespace std;

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
    }
} setupio;

int main() {
    lint x, n;
    cin >> x >> n;
    lint pos;
    lint l = 0, r = 1500000000;
    while (r - l > 1) {
        lint mid = (l + r) / 2;
        lint sum = mid * (mid + 1) / 2;
        (abs(x) < sum ? r : l) = mid;
    }
    pos = l;
    lint ans;
    if (n <= pos) {
        lint sum = n * (n + 1) / 2;
        ans = (x <= 0 ? x + sum : x - sum);
    } else {
        lint sum = l * (l + 1) / 2;
        lint val = (x <= 0 ? x + sum : x - sum);
        if (n % 2 != pos % 2) {
            pos++;
            val += (val <= 0 ? pos : -pos);
        }
        lint k = (n - pos) / 2;
        ans = (val <= 0 ? val - k : val + k);
    }
    cout << ans << "\n";
}