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

namespace AtCoder
{
    class Program
    {
        static int MODBASE = 1000000007;
        static void Main(string[] args)
        {
            int[] hw = Console.ReadLine().Split(' ').Select(v => int.Parse(v)).ToArray();
            int h = hw[0];
            int w = hw[1];

            char[][] grid = new char[h][];
            for (int i = 0; i < h; i++)
            {
                grid[i] = Console.ReadLine().ToCharArray();
            }

            int[][] horizontalSpace = new int[h][];

            // 横方向の連続空きマス
            for (int i = 0; i < h; i++)
            {
                // とりあえず順方向にすすんでカウント
                int currentSpace = 0;
                horizontalSpace[i] = new int[w];
                for (int j = 0; j < w; j++)
                {
                    if(grid[i][j] == '#')
                    {
                        currentSpace = 0;
                        horizontalSpace[i][j] = 0;
                    }
                    else
                    {
                        currentSpace++;
                        horizontalSpace[i][j] = currentSpace;
                    }
                }
                // 逆方向に進んで最大値で上書き
                currentSpace = 0;
                for (int j = w - 1; j >= 0; j--)
                {
                    if (grid[i][j] == '#')
                    {
                        currentSpace = 0;
                        horizontalSpace[i][j] = 0;
                    }
                    else
                    {
                        if (currentSpace == 0)
                        {
                            currentSpace = horizontalSpace[i][j];
                        }
                        horizontalSpace[i][j] = currentSpace;
                    }
                }
            }

            int[][] verticalSpace = new int[h][];

            // 縦方向の連続空きマス
            for (int i = 0; i < h; i++)
            {
                verticalSpace[i] = new int[w];
            }

            for (int j = 0; j < w; j++)
            {
                // とりあえず順方向にすすんでカウント
                int currentSpace = 0;
                for (int i = 0; i < h; i++)
                {
                    if (grid[i][j] == '#')
                    {
                        currentSpace = 0;
                        verticalSpace[i][j] = 0;
                    }
                    else
                    {
                        currentSpace++;
                        verticalSpace[i][j] = currentSpace;
                    }
                }
                // 逆方向に進んで最大値で上書き
                currentSpace = 0;
                for (int i = h - 1; i >= 0; i--)
                {
                    if (grid[i][j] == '#')
                    {
                        currentSpace = 0;
                        verticalSpace[i][j] = 0;
                    }
                    else
                    {
                        if (currentSpace == 0)
                        {
                            currentSpace = verticalSpace[i][j];
                        }
                        verticalSpace[i][j] = currentSpace;
                    }
                }
            }

            int maxSpace = 0;
            for (int i = 0; i < h; i++)
            {
                for(int j = 0; j < w; j++)
                {
                    maxSpace = Math.Max(maxSpace, horizontalSpace[i][j] + verticalSpace[i][j]);
                }
            }

            ShowAnswer(maxSpace - 1);
        }

        static void ShowAnswer(string answer)
        {
            Console.WriteLine(answer);
        }

        static void ShowAnswer(int answer)
        {
            ShowAnswer(answer.ToString());
        }

        /*
         * デバッグ用コード
         */
        static void DebugPrint(string str)
        {
            // Console.WriteLine(str);
        }

        static void DebugPrint(char[] charay)
        {
            DebugPrint(new string(charay));
        }

        static void DebugPrint(int[] intaray)
        {
            DebugPrint(string.Join(" ", intaray));
        }
    }
}

Measured memory_bytes: 62392