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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll x, n;
    cin >> x >> n;
    ll ok = 0, ng = 1ll << 31;
    while(ok + 1 < ng){
        ll mid = (ok + ng) / 2;
        ll s = mid * (mid + 1) / 2;
        (s <= abs(x) ? ok : ng) = mid;
    }
    if(n <= ok){
        if(x > 0){
            x -= n * (n + 1) / 2;
        }else{
            x += n * (n + 1) / 2;
        }
        cout << x << '\n';
        return 0;
    }
    if(x > 0){
        x -= ok * (ok + 1) / 2;
    }else{
        x += ok * (ok + 1) / 2;
    }
    //cerr << x << " " << ok << '\n';
    // ok + 1 -> n
    ll len = n - ok;
    if(len & 1){
        if(x > 0){
            x -= ok + 1;
        }else{
            x += ok + 1;
        }
    }
    if(x > 0){
        x += len / 2;
    }else{
        x -= len / 2;
    }
    cout << x << '\n';
}