using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using SB = System.Text.StringBuilder;
//using System.Numerics;
using static System.Math;
using Number = System.Int32;
namespace Program {
    public class Solver {
        Random rnd = new Random();
        public void Solve() {
            var n = ri;
            var m = ri;
            var a = new long[n];
            for (int i = 0; i < n - 1; i++)
                a[i + 1] = a[i] + rl;
            var b = Enumerate(n, x => new long[m]);
            for (int i = 0; i < n; i++)
                for (int j = 0; j < m; j++)
                    b[i][j] = rl;
            var imos = Enumerate(5002, x => new long[5002]);
            var C = new long[n];

            for (int j = 0; j < m; j++)
            {
                for (int i = 0; i < n; i++)
                    C[i] = b[i][j] * n + i;
                Array.Sort(C);
                //Array.Reverse(C);
                var left = new int[n];
                var right = new int[n];
                for (int i = 0; i < n; i++)
                {
                    left[i] = i - 1; right[i] = i + 1;
                }
                foreach (var x in C)
                {
                    var v = x / n;
                    var pos = (int)(x % n);
                    var next = right[pos];
                    var pre = left[pos] + 1;
                    imos[pre][pos] += v;
                    imos[pre][next] -= v;
                    imos[pos + 1][pos] -= v;
                    imos[pos + 1][next] += v;
                    if (pre != 0)
                        right[pre - 1] = next;
                    if (next != n) left[next] = pre - 1;
                }
            }
            for (int j = 0; j <= n; j++)
                for (int i = 0; i <= n; i++)
                    imos[i][j + 1] += imos[i][j];
            for (int i = 0; i <= n; i++)
                for (int j = 0; j <= n; j++)
                    imos[i + 1][j] += imos[i][j];
            foreach (var x in imos) Debug.WriteLine(x.AsJoinedString());

            var max = 0L;
            for (int i = 0; i < n; i++)
                for (int j = i; j < n; j++)
                    max = Math.Max(max, imos[i][j] - (a[j] - a[i]));
            Console.WriteLine(max);



        }
        const long INF = 5L << 60;
        static int[] dx = { -1, 0, 1, 0 };
        static int[] dy = { 0, 1, 0, -1 };
        int ri { get { return sc.Integer(); } }
        long rl { get { return sc.Long(); } }
        double rd { get { return sc.Double(); } }
        string rs { get { return sc.Scan(); } }
        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());

        static T[] Enumerate<T>(int n, Func<int, T> f) {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f(i);
            return a;
        }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region main
static class Ex {
    static public string AsString(this IEnumerable<char> ie) { return new string(ie.ToArray()); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") {
        return string.Join(st, ie);
    }
    static public void Main() {
        Console.SetOut(new Program.IO.Printer(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Program.Solver();
        try
        {
            solver.Solve();
            Console.Out.Flush();
        }
        catch { }
    }
}
#endregion
#region Ex
namespace Program.IO {
    using System.IO;
    using System.Text;
    using System.Globalization;

    public class Printer: StreamWriter {
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
    }

    public class StreamScanner {
        public StreamScanner(Stream stream) { str = stream; }

        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }

        private byte read() {
            if (isEof) return 0;
            if (ptr >= len)
            {
                ptr = 0;
                if ((len = str.Read(buf, 0, 1024)) <= 0)
                {
                    isEof = true;
                    return 0;
                }
            }
            return buf[ptr++];
        }

        public char Char() {
            byte b = 0;
            do b = read(); while ((b < 33 || 126 < b) && !isEof);
            return (char)b;
        }
        public string Scan() {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read()) sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine() {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n' && b != 0; b = (char)read()) if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long() { return isEof ? long.MinValue : long.Parse(Scan()); }
        public int Integer() { return isEof ? int.MinValue : int.Parse(Scan()); }
        public double Double() { return isEof ? double.NaN : double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
}

#endregion


#region Set
public class Set<T> {
    Node root;
    readonly IComparer<T> comparer;
    readonly Node nil;
    public bool IsMultiSet { get; set; }
    public Set(IComparer<T> comparer) {
        nil = new Node(default(T));
        root = nil;
        this.comparer = comparer;
    }
    public Set(Comparison<T> comaprison) : this(Comparer<T>.Create(comaprison)) { }
    public Set() : this(Comparer<T>.Default) { }
    public bool Add(T v) {
        return insert(ref root, v);
    }
    public bool Remove(T v) {
        return remove(ref root, v);
    }
    public T this[int index] { get { return find(root, index); } }
    public int Count { get { return root.Count; } }
    public void RemoveAt(int k) {
        if (k < 0 || k >= root.Count) throw new ArgumentOutOfRangeException();
        removeAt(ref root, k);
    }
    public T[] Items {
        get {
            var ret = new T[root.Count];
            var k = 0;
            walk(root, ret, ref k);
            return ret;
        }
    }
    void walk(Node t, T[] a, ref int k) {
        if (t.Count == 0) return;
        walk(t.lst, a, ref k);
        a[k++] = t.Key;
        walk(t.rst, a, ref k);
    }

    bool insert(ref Node t, T key) {
        if (t.Count == 0) { t = new Node(key); t.lst = t.rst = nil; t.Update(); return true; }
        var cmp = comparer.Compare(t.Key, key);
        bool res;
        if (cmp > 0)
            res = insert(ref t.lst, key);
        else if (cmp == 0)
        {
            if (IsMultiSet) res = insert(ref t.lst, key);
            else return false;
        }
        else res = insert(ref t.rst, key);
        balance(ref t);
        return res;
    }
    bool remove(ref Node t, T key) {
        if (t.Count == 0) return false;
        var cmp = comparer.Compare(key, t.Key);
        bool ret;
        if (cmp < 0) ret = remove(ref t.lst, key);
        else if (cmp > 0) ret = remove(ref t.rst, key);
        else
        {
            ret = true;
            var k = t.lst.Count;
            if (k == 0) { t = t.rst; return true; }
            if (t.rst.Count == 0) { t = t.lst; return true; }


            t.Key = find(t.lst, k - 1);
            removeAt(ref t.lst, k - 1);
        }
        balance(ref t);
        return ret;
    }
    void removeAt(ref Node t, int k) {
        var cnt = t.lst.Count;
        if (cnt < k) removeAt(ref t.rst, k - cnt - 1);
        else if (cnt > k) removeAt(ref t.lst, k);
        else
        {
            if (cnt == 0) { t = t.rst; return; }
            if (t.rst.Count == 0) { t = t.lst; return; }

            t.Key = find(t.lst, k - 1);
            removeAt(ref t.lst, k - 1);
        }
        balance(ref t);
    }
    void balance(ref Node t) {
        var balance = t.lst.Height - t.rst.Height;
        if (balance == -2)
        {
            if (t.rst.lst.Height - t.rst.rst.Height > 0) { rotR(ref t.rst); }
            rotL(ref t);
        }
        else if (balance == 2)
        {
            if (t.lst.lst.Height - t.lst.rst.Height < 0) rotL(ref t.lst);
            rotR(ref t);
        }
        else t.Update();
    }

    T find(Node t, int k) {
        if (k < 0 || k > root.Count) throw new ArgumentOutOfRangeException();
        for (; ; )
        {
            if (k == t.lst.Count) return t.Key;
            else if (k < t.lst.Count) t = t.lst;
            else { k -= t.lst.Count + 1; t = t.rst; }
        }
    }
    public int LowerBound(T v) {
        var k = 0;
        var t = root;
        for (; ; )
        {
            if (t.Count == 0) return k;
            if (comparer.Compare(v, t.Key) <= 0) t = t.lst;
            else { k += t.lst.Count + 1; t = t.rst; }
        }
    }
    public int UpperBound(T v) {
        var k = 0;
        var t = root;
        for (; ; )
        {
            if (t.Count == 0) return k;
            if (comparer.Compare(t.Key, v) <= 0) { k += t.lst.Count + 1; t = t.rst; }
            else t = t.lst;
        }
    }

    void rotR(ref Node t) {
        var l = t.lst;
        t.lst = l.rst;
        l.rst = t;
        t.Update();
        l.Update();
        t = l;
    }
    void rotL(ref Node t) {
        var r = t.rst;
        t.rst = r.lst;
        r.lst = t;
        t.Update();
        r.Update();
        t = r;
    }


    class Node {
        public Node(T key) {
            Key = key;
        }
        public int Count { get; private set; }
        public sbyte Height { get; private set; }
        public T Key { get; set; }
        public Node lst, rst;
        public void Update() {
            Count = 1 + lst.Count + rst.Count;
            Height = (sbyte)(1 + Math.Max(lst.Height, rst.Height));
        }
        public override string ToString() {
            return string.Format("Count = {0}, Key = {1}", Count, Key);
        }
    }
}
#endregion

#region FenwickTree
public class FenwickTree {
    int n;
    Number[] bit;
    int max = 1;
    public FenwickTree(int size) {
        n = size; bit = new Number[n + 1];
        while ((max << 1) <= n) max <<= 1;
    }
    /// <summary>sum[a,b]</summary>
    public Number this[int i, int j] { get { return this[j] - this[i - 1]; } }
    /// <summary>sum[0,i]</summary>
    public Number this[int i] { get { Number s = 0; for (; i > 0; i -= i & -i) s += bit[i]; return s; } }
    public int LowerBound(Number w) {
        if (w <= 0) return 0;
        int x = 0;
        for (int k = max; k > 0; k >>= 1)
            if (x + k <= n && bit[x + k] < w)
            {
                w -= bit[x + k];
                x += k;
            }
        return x + 1;
    }
    /// <summary>add v to bit[i]</summary>
    public void Add(int i, Number v) {
        Debug.Assert(i >= 1);
        for (; i <= n; i += i & -i) bit[i] += v;
    }
    public Number[] Items {
        get {
            var ret = new Number[n + 1];
            for (int i = 0; i < ret.Length; i++)
                ret[i] = this[i, i];
            return ret;
        }
    }
}
#endregion

Measured memory_bytes: 237188