#include<bits/stdc++.h>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define pb push_back
#define all(a) begin(a),end(a)
#define allr(a) rbegin(a),rend(a)
#define ff first
#define ss second
template<class T> bool chmax(T& a,T b){return a<b?a=b,1:0;}
template<class T> bool chmin(T& a,T b){return a>b?a=b,1:0;}
using ll =long long;
using pii =pair<int,int>;
using pll=pair<long long,long long>;
using vi=vector<int>;
using vll=vector<ll>;
inline bool ingrid(int a,int b,int h,int w){
    return 0<=a&&a<h&&0<=b&&b<w;
}

const int INFI = numeric_limits<int>::max() / 2; const long long INFL = numeric_limits<long long>::max() / 2;
constexpr pii dx4[4] = {pii{-1, 0}, pii{0, -1},pii{1, 0}, pii{0, 1} };
#define endl '\n'
ll x,n;
void solve(){
    if(x<=0){
        ll ok=0,ng=n+1;
        while(abs(ok-ng)>1){
            ll mid=(ok+ng)/2;
            double p=mid;p=p*(p+1)/2;
            if(p>=1e19)ng=mid;
            else if(((mid&1)?(mid+1)/2*mid:mid/2*(mid+1))+x<=0)ok=mid;
            else ng=mid;
        }
        ll ans=((ok&1)?(ok+1)/2*ok:ok/2*(ok+1))+x;
        ans-=(n-ok)/2;
        if((n-ok)&1){
            ans+=n;
        }
        cout<<ans<<endl;
    }else{
        ll ok=0,ng=n+1;
        while(abs(ok-ng)>1){
            ll mid=(ok+ng)/2;
            double p=mid;p=p*(p+1)/2;
            if(p>=1e19)ng=mid;
            else if(x-((mid&1)?(mid+1)/2*mid:mid/2*(mid+1))>0)ok=mid;
            else ng=mid;
        }
        ll ans=x-((ok&1)?(ok+1)/2*ok:ok/2*(ok+1));
        ans+=(n-ok)/2;
        if((n-ok)&1){
            ans-=n;
        }
        cout<<ans<<endl;
    }
}

int main(){
    cin>>x>>n;
    solve();
    return 0;
}
/*

*/