// #include <bits/allocator.h> // Temp fix for gcc13 global pragma
// #pragma GCC target("avx2,bmi2,popcnt,lzcnt")
// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
#if __cplusplus >= 202002L
using namespace numbers;
#endif
#ifdef LOCAL
	#include "Debug.h"
#else
	#define debug_endl() 42
	#define debug(...) 42
	#define debug2(...) 42
	#define debugbin(...) 42
#endif



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	long long x, n;
	cin >> x >> n;
	long long t = *ranges::partition_point(ranges::iota_view(0LL, n + 1), [&](long long t){ return abs(x) > __int128_t(1) * t * (t + 1) / 2; }) - 1;
	if(t == n){
		cout << (abs(x) - n * (n + 1) / 2) * (x >= 0 ? 1 : -1) << "\n";
		return 0;
	}
	long long cur = abs(x) - t * (t + 1) / 2 + (n - (t + 1) + 1) / 2;
	if(n - (t + 1) + 1 & 1){
		cur -= n;
	}
	cout << cur * (x >= 0 ? 1 : -1) << "\n";
	return 0;
}

/*

*/