Problem:
Score : 200 points

Problem Statement

You have N apples, called Apple 1, Apple 2, Apple 3, ..., Apple N. The flavor of Apple i is L+i-1, which can be negative.

You can make an apple pie using one or more of the apples. The flavor of the apple pie will be the sum of the flavors of the apples used.

You planned to make an apple pie using all of the apples, but being hungry tempts you to eat one of them, which can no longer be used to make the apple pie.

You want to make an apple pie that is as similar as possible to the one that you planned to make. Thus, you will choose the apple to eat so that the flavor of the apple pie made of the remaining N-1 apples will have the smallest possible absolute difference from the flavor of the apple pie made of all the N apples.

Find the flavor of the apple pie made of the remaining N-1 apples when you choose the apple to eat as above.

We can prove that this value is uniquely determined.

Constraints

2 \leq N \leq 200

-100 \leq L \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N L

Output

Find the flavor of the apple pie made of the remaining N-1 apples when you optimally choose the apple to eat.

Sample Input 1

5 2

Sample Output 1

18

The flavors of Apple 1, 2, 3, 4, and 5 are 2, 3, 4, 5, and 6, respectively. The optimal choice is to eat Apple 1, so the answer is 3+4+5+6=18.

Sample Input 2

3 -1

Sample Output 2

0

The flavors of Apple 1, 2, and 3 are -1, 0, and 1, respectively. The optimal choice is to eat Apple 2, so the answer is (-1)+1=0.

Sample Input 3

30 -50

Sample Output 3

-1044

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using Extensions;
using static System.Math;
using static Extensions.MathExtension;
using static Extensions.ConsoleInputExtension;
using static Extensions.ConsoleOutputExtension;

class Solver
{
    public void Solve()
    {
        //Solve Code Here
        int N = Cin, L = Cin;

        int max = int.MinValue;
        for (int i = 0; i < N; i++)
        {
            int sum = 0;
            for (int r = 0; r < N; r++)
            {
                if (i != r) sum += L + r;
            }

            max = Max(max, sum);
        }

        Coutln(max);
    }

    //Other Functions Here
}

class EntryPoint
{
    static void Main(string[] args)
    {
        new Solver().Solve();
        Flush();
    }
}

class PriorityQueue<T>
{
    private readonly List<Tuple<int, T>> _list = new List<Tuple<int, T>>();

    public PriorityQueue()
    {
    }

    public void Push(T item, int priority)
    {
        var itemIndex = _list.Count;
        _list.Add(Tuple.Create(priority, item));
        int parentIndex;
        while ((parentIndex = GetParentIndex(itemIndex)) != -1 && priority > _list[parentIndex].Item1)
        {
            Swap(itemIndex, parentIndex);
            itemIndex = parentIndex;
        }
    }

    private int GetParentIndex(int index)
    {
        if (index == 0) return -1;
        return ((index + 1) >> 1) - 1;
    }

    private Tuple<int, int> GetChildrenIndex(int index)
    {
        var item2 = (index + 1) << 1;
        var item1 = item2 - 1;
        return item2 >= _list.Count ? null : Tuple.Create(item1, item2);
    }

    public T Pop()
    {
        var item = _list[0].Item2;
        Tuple<int, int> childrenIndex;
        int index = 0;
        while ((childrenIndex = GetChildrenIndex(index)) != null)
        {
            if (_list[childrenIndex.Item1].Item1 > _list[childrenIndex.Item2].Item1)
                _list[index] = _list[childrenIndex.Item1];
            else
                _list[index] = _list[childrenIndex.Item2];
        }

        return item;
    }

    public T Peek()
    {
        return _list[0].Item2;
    }

    private void Swap(int index1, int index2)
    {
        var tmp = _list[index1];
        _list[index1] = _list[index2];
        _list[index2] = tmp;
    }
}

struct Rational
{
    private long _numerator;
    private long _denominator;
    public long Numerator => _numerator;
    public long Denominator => _denominator;

    public Rational(long numerator, long denominator)
    {
        var gcd = GCD(numerator, denominator);
        _numerator = numerator     / gcd;
        _denominator = denominator / gcd;
    }

    public static Rational operator +(Rational a, Rational b)
    {
        return new Rational(a._numerator * b._denominator + b._numerator * a._denominator,
                            a._denominator * b._denominator);
    }

    public static Rational operator -(Rational a, Rational b)
    {
        return new Rational(a._numerator * b._denominator - b._numerator * a._denominator,
                            a._denominator * b._denominator);
    }

    public static Rational operator *(Rational a, Rational b)
    {
        return new Rational(a._numerator * b._numerator, a._denominator * b._denominator);
    }

    public static Rational operator /(Rational a, Rational b)
    {
        return new Rational(a._numerator * b._denominator, a._denominator * b._numerator);
    }

    public static explicit operator Rational(int i)
    {
        return new Rational(i, 1);
    }

    public static explicit operator Rational(long l)
    {
        return new Rational(l, 1);
    }

    public static explicit operator Rational(double d)
    {
        long denominator = 1;
        while (d % 1 != 0)
        {
            denominator *= 2;
            d *= 2;
        }

        return new Rational((long) d, denominator);
    }

    public static explicit operator Rational(float f)
    {
        long denominator = 1;
        while (f % 1 != 0)
        {
            denominator *= 2;
            f *= 2;
        }

        return new Rational((long) f, denominator);
    }
}

class UnionFind
{
    private readonly int[] _array;

    public UnionFind(int N)
    {
        _array = new int[N];
        for (int i = 0; i < N; i++)
        {
            _array[i] = i;
        }
    }

    public int GetRootNode(int n)
    {
        if (_array[n] == n) return n;
        return _array[n] = GetRootNode(_array[n]);
    }

    public void UnionGroup(int a, int b)
    {
        var rootA = GetRootNode(a);
        var rootB = GetRootNode(b);
        if (rootA == rootB) return;
        _array[rootA] = rootB;
    }

    public bool IsSameGroup(int a, int b) => GetRootNode(a) == GetRootNode(b);

    public bool IsRoot(int n) => _array[n] == n;
}


namespace Extensions
{
    public class ConsoleInputExtension
    {
        private static readonly ConsoleInputExtension _cin = new ConsoleInputExtension();

        public static ConsoleInputExtension Cin => _cin;

        private static readonly Queue<string> _inputQueue = new Queue<string>();

        private ConsoleInputExtension()
        {
        }

        public static implicit operator string(ConsoleInputExtension _)
        {
            if (_inputQueue.Count == 0) Console.ReadLine().Split(' ').ForEach(val => _inputQueue.Enqueue(val));
            return _inputQueue.Dequeue();
        }

        public static implicit operator int(ConsoleInputExtension _)
        {
            if (_inputQueue.Count == 0) Console.ReadLine().Split(' ').ForEach(val => _inputQueue.Enqueue(val));
            return int.Parse(_inputQueue.Dequeue());
        }

        public static implicit operator long(ConsoleInputExtension _)
        {
            if (_inputQueue.Count == 0) Console.ReadLine().Split(' ').ForEach(val => _inputQueue.Enqueue(val));
            return long.Parse(_inputQueue.Dequeue());
        }

        public static implicit operator float(ConsoleInputExtension _)
        {
            if (_inputQueue.Count == 0) Console.ReadLine().Split(' ').ForEach(val => _inputQueue.Enqueue(val));
            return float.Parse(_inputQueue.Dequeue());
        }

        public static implicit operator double(ConsoleInputExtension _)
        {
            if (_inputQueue.Count == 0) Console.ReadLine().Split(' ').ForEach(val => _inputQueue.Enqueue(val));
            return double.Parse(_inputQueue.Dequeue());
        }
    }

    public static class ConsoleOutputExtension
    {
        private static StreamWriter _writer = new StreamWriter(Console.OpenStandardOutput()) {AutoFlush = false};

        public static void Cout(object o)
        {
            _writer.Write(o);
        }

        public static void CoutF(object o)
        {
            _writer.Write(o);
            _writer.Flush();
        }

        public static void Coutln(object o)
        {
            _writer.WriteLine(o);
        }

        public static void CoutlnF(object o)
        {
            _writer.WriteLine(o);
            _writer.Flush();
        }

        public static void Flush()
        {
            _writer.Flush();
        }
    }

    public static class MathExtension
    {
        //最小公倍数
        public static int LCM(int num1, int num2)
        {
            var gcd = GCD(num1, num2);
            return num1 * (num2 / gcd);
        }

        public static long LCM(long num1, long num2)
        {
            var gcd = GCD(num1, num2);
            return num1 * (num2 / gcd);
        }

        //最大公約数
        public static int GCD(int num1, int num2)
        {
            int a = Math.Max(num1, num2);
            int b = Math.Min(num1, num2);
            int mod;
            while ((mod = a % b) != 0)
            {
                a = b;
                b = mod;
            }

            return b;
        }

        public static long GCD(long num1, long num2)
        {
            long a = Math.Max(num1, num2);
            long b = Math.Min(num1, num2);
            long mod;
            while ((mod = a % b) != 0)
            {
                a = b;
                b = mod;
            }

            return b;
        }
    }

    public static class EnumerableExtension
    {
        public delegate void Function<in T>(T val);

        public static void ForEach<T>(this IEnumerable<T> enumerable, Function<T> function)
        {
            foreach (var x in enumerable)
            {
                function(x);
            }
        }
    }
}