using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static Scanner sc = new Scanner();
    static void Main(string[] args)
    {
        var H = sc.ReadInt();
        var W = sc.ReadInt();
        var S = sc.ReadStrArray(H);

        var t = new L[H, W];
        var ans = 0L;

        for (int h = 0; h < H; h++)
        {
            for (int w = 0; w < W; w++)
            {
                if (S[h][w] == '#') t[h, w].X = 0;
                else if (w == 0 || t[h, w - 1].X == 0)
                {
                    var count = 0;
                    for (int i = w; i < W; i++)
                    {
                        if (S[h][i] == '.') count++;
                        else break;
                    }
                    t[h, w].X = count;
                }
                else
                {
                    t[h, w].X = t[h, w - 1].X;
                }
            }
        }
        for (int w = 0; w < W; w++)
        {
            for (int h = 0; h < H; h++)
            {
                if (S[h][w] == '#') t[h, w].Y = 0;
                else if (h == 0 || t[h - 1, w].Y == 0)
                {
                    var count = 0;
                    for (int i = h; i < H; i++)
                    {
                        if (S[i][w] == '.') count++;
                        else break;
                    }
                    t[h, w].Y = count;
                }
                else
                {
                    t[h, w].Y = t[h - 1, w].Y;
                }
                ans = Math.Max(ans, t[h, w].Sum);
            }
        }

        Console.WriteLine(ans);
    }
    struct L
    {
        public long X { get; set; }
        public long Y { get; set; }
        public long Sum { get { return this.X + this.Y - 1; } }
        public L(long x, long y)
        {
            this.X = x;
            this.Y = y;
        }
    }
}

class Modulo
{
    public readonly int MOD;
    private readonly List<int> Facs = new List<int>() { 1 };

    public Modulo(int mod = 1000000007) { this.MOD = mod; }
    public int Mul(int a, int b) { return (int)(Math.BigMul(a, b) % MOD); }
    public int Div(int a, int b) { return Mul(a, Pow(b, MOD - 2)); }
    public int Pow(int a, int n)
    {
        switch (n)
        {
            case 0:
                return 1;
            case 1:
                return a;
            default:
                int p1 = Pow(a, n / 2);
                int p2 = Mul(p1, p1);
                return ((n % 2) == 0) ? p2 : Mul(p2, a);
        }
    }
    public int Fac(int n)
    {
        for (int i = this.Facs.Count; i <= n; i++)
        {
            this.Facs.Add(Mul(i, Facs[i - 1]));
        }
        return this.Facs[n];
    }
    public int nPr(int n, int r) => Div(Fac(n), Fac(n - r));
    public int nCr(int n, int r)
    {
        if (n < r) return 0;
        if (n == r) return 1;
        int res = Fac(n);
        res = Div(res, Fac(r));
        res = Div(res, Fac(n - r));
        return res;
    }
}

class Debug
{
    public static void Dump<T>(T[,] array)
    {
        Console.WriteLine();
        var h = array.GetLength(0);
        var w = array.GetLength(1);

        for (int r = 0; r < h; r++)
        {
            for (int c = 0; c < w; c++)
            {
                Console.Write(array[r, c]);
                Console.Write(" ");
            }
            Console.WriteLine();
        }
        Console.WriteLine();
    }
    public static void Dump<T>(T[] array)
    {
        Console.WriteLine();
        Console.WriteLine(string.Join(" ", array));
        Console.WriteLine();
    }
}

class Scanner
{
    string[] S = new string[0];
    int Index = 0;
    char[] Separators = new char[] { ' ' };

    public string Next()
    {
        if (this.Index < this.S.Length) return this.S[this.Index++];
        var line = "";
        while (line == "") line = Console.ReadLine();
        this.S = line.Split(this.Separators, StringSplitOptions.RemoveEmptyEntries);
        if (this.S.Length == 0) return this.Next();
        this.Index = 0;
        return this.S[this.Index++];
    }

    public string ReadStr()
    {
        return this.Next();
    }

    public char ReadChar()
    {
        return this.Next()[0];
    }

    public int ReadInt()
    {
        return int.Parse(this.Next());
    }

    public uint ReadUInt()
    {
        return uint.Parse(this.Next());
    }

    public long ReadLong()
    {
        return long.Parse(this.Next());
    }

    public int[] ReadIntArray(int n)
    {
        var array = new int[n];
        for (int i = 0; i < array.Length; i++)
        {
            array[i] = this.ReadInt();
        }
        return array;
    }

    public long[] ReadLongArray(int n)
    {
        var array = new long[n];
        for (int i = 0; i < array.Length; i++)
        {
            array[i] = this.ReadLong();
        }
        return array;
    }

    public char[] ReadCharArray(int n)
    {
        var array = new char[n];
        for (int i = 0; i < array.Length; i++)
        {
            array[i] = this.ReadChar();
        }
        return array;
    }

    public string[] ReadStrArray(int n)
    {
        var array = new string[n];
        for (int i = 0; i < array.Length; i++)
        {
            array[i] = this.ReadStr();
        }
        return array;
    }
}

class HashMap<K, V> : Dictionary<K, V> where V : new()
{
    private V DefaltValue = new V();
    public HashMap() { }
    public HashMap(V defaultValue)
    {
        this.DefaltValue = new V();
    }
    new public V this[K i]
    {
        get
        {
            V v;
            return TryGetValue(i, out v) ? v : base[i] = this.DefaltValue;
        }
        set { base[i] = value; }
    }
}

Measured memory_bytes: 94648