#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
namespace mp = boost::multiprecision;
using Bint = mp::cpp_int;
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    Bint x, n;
    cin >> x >> n;
    Bint sum = Bint(n)*Bint(n+1)/2;
    if(abs(x)>sum) {
        if(x>0) cout << x-sum << endl;
        else cout << sum+x << endl;
        return 0;
    }
    Bint l = 0;
    Bint r = n;
    while(r-l>1) {
        Bint mid = (l+r)/2;
        if(mid*(mid+1)/2>abs(x)) r = mid;
        else l = mid;
    }
    if(x>0) {
        x -= l*(l+1)/2;  
        if((n-l)%2) {
            x -= l+1;
            x -= (n-l)/2;
        }      
        else{
            x += (n-l)/2;
        }
        cout << x << endl;
    }
    else{
        x += l*(l+1)/2;  
        if((n-l)%2) {
            x += l+1;
            x += (n-l)/2;
        }      
        else{
            x -= (n-l)/2;
        }
        cout << x << endl;
    }
    return 0;
}