#include <bits/stdc++.h>
#include <bits/stdc++.h>
#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/modint>
// using namespace atcoder;
// using mint = modint998244353;
using ll = long long;
#define fix(x) fixed << setprecision(x)
#define rep(i, n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll x,n,ans;
    cin >> x >> n;
    bool f = (x<=0);
    if(f) x = -x+1;
    ll l = 0, r = 2e9;
    while(l+1<r){
        ll md = (l+r)/2;
        if(md*(md+1)/2<x) l = md;
        else r = md; 
    }
    if(n<=r) ans = x - n*(n+1)/2;
    else{
        x -= l*(l+1)/2;
        n -= l;
        if(n&1) ans = x - r - n/2;
        else ans = x + n/2;
    }
    if(f) ans = -ans+1;
    cout << ans << '\n';
    return 0;
}