#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define vi vector<int>
#define vl vector<ll>
#define vii vector<pair<int,int>>
#define vll vector<pair<ll,ll>>
#define vvi vector<vector<int>>
#define vvl vector<vector<ll>>
#define vvii vector<vector<pair<int,int>>>
#define vvll vector<vector<pair<ll,ll>>>
#define vst vector<string>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define mkunique(x) sort(all(x));(x).erase(unique(all(x)),(x).end())
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005,INF=15<<26;

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    ll x,n;cin>>x>>n;
    ll l=0,r=2e9;
    while(r-l>1){
        ll m=(l+r)/2;
        if(m*(m+1)/2>abs(x)) r=m;
        else l=m;
    }
    if(r>=n){
        ll sum=n*(n+1)/2;
        if(x<=0) cout<<x+sum<<"\n";
        else cout<<x-sum<<"\n";
    }else{
        ll now;
        if(x<=0) now=x+r*(r+1)/2;
        else now=x-r*(r+1)/2;
        
        ll rem=n-r,st=r+1;
        if(rem&1){
            if(now>0) now-=st;
            else now+=st;
            rem--;
            st++;
        }
        if(now>0){
            now+=rem/2;
        }else{
            now-=rem/2;
        }
        cout<<now<<"\n";
    }
}