using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Diagnostics;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Numerics;
using System.IO;
using System.Runtime.InteropServices;
using static System.Math;
using static Math2;
using static io;
using static Utils;



public class CompetitiveProgramming
{

  public void Solve()
  {
    var o = Ints;
    var H = o[0];
    var W = o[1];
    var S = new char[H][];
    for (int i = 0; i < H; ++i)
    {
      S[i] = Chars;
    }
    var huf = new UnionFind(H * W);
    var wuf = new UnionFind(W * H);
    for (int i = 0; i < H; ++i)
    {
      for (int j = 1; j < W; ++j)
      {
        if (S[i][j] != '#' && S[i][j - 1] != '#')
        {
          huf.Merge(i * W + j, i * W + j - 1);
        }
      }
    }
    for (int j = 0; j < W; ++j)
    {
      for (int i = 1; i < H; ++i)
      {
        if (S[i][j] != '#' && S[i - 1][j] != '#')
        {
          wuf.Merge(i * W + j, (i - 1) * W + j);
        }
      }
    }

    long ans = 0;
    for (int i = 0; i < H; ++i)
    {
      for (int j = 0; j < W; ++j)
      {
        if (S[i][j] == '#') continue;
        int sum = huf.Size(i * W + j) + wuf.Size(i * W + j) - 1;
        ans = Max(ans, sum);
      }
    }

    Write(ans);

  }
}
public class UnionFind
{
  int _count;
  int[] par, sizes, rank;
  public UnionFind(int N)
  {
    _count = N;
    par = new int[N];
    sizes = new int[N];
    rank = new int[N];
    for (int i = 0; i < N; ++i)
    {
      par[i] = i;
      sizes[i] = 1;
      rank[i] = 0;
    }
  }
  int Root(int X)
  {
    if (par[X] == X)
    {
      return X;
    }
    else return (par[X] = Root(par[X]));
  }
  public bool Merge(int X, int Y)
  {
    X = Root(X);
    Y = Root(Y);
    if (X == Y) return false;
    --_count;
    if (rank[X] < rank[Y])
    {
      par[X] = Y;
      sizes[Y] += sizes[X];
    }
    else
    {
      par[Y] = X;
      sizes[X] += sizes[Y];
      if (rank[X] == rank[Y]) ++rank[X];
    }
    return true;
  }
  public bool IsSame(int X, int Y) => Root(X) == Root(Y);
  public int Count => _count;
  public bool IsParent(int X) => X == Root(X);
  public int GetParent(int X) => Root(X);
  public int Size(int X) => sizes[Root(X)];
}

public static class Math2
{
  public const int INF = 1 << 29;
  public const long INFL = 1L << 60;
  public const long MOD = 1000000007;
  public const int MOD2 = 998244353;

  public static long Power(long a, long b, long MOD = 1000000007)//i^N
  {
    long res = 1;
    while (b > 0)
    {
      if ((b & 1) != 0) res = res * a % MOD;
      a = a * a % MOD;
      b >>= 1;
    }
    return res;
  }
  public static long Power2(long a, long b)//i^N
  {
    long res = 1;
    while (b > 0)
    {
      if ((b & 1) != 0) res = res * a;
      a = a * a;
      b >>= 1;
    }
    return res;
  }
  public static long GCD(long a, long b)
  {
    while (b > 0)
    {
      var r = a % b;
      a = b;
      b = r;
    }
    return a;
  }
  public static long LCM(long a, long b) => (b / GCD(a, b)) * a;
  public static long Comb(long n, long r, int MOD = 1000000007)
  {
    long ret = 1;
    long x = 1;
    for (long i = n; i >= n - r + 1; --i)
    {
      ret = ret / x * i;
      ret %= MOD;
      x++;
    }
    return ret;
  }
  public static long Comb2(long n, long r)
  {
    long Nume = 1;
    long Deno = 1;

    if (r > n - r) r = n - r;
    for (long i = 1; i <= r; ++i)
    {
      Deno *= i;
      Nume *= n - i + 1;
    }
    return Nume / Deno;
  }
}
public static class Utils
{

  public static void Swap<T>(ref T A, ref T B)
  {
    T x = A;
    A = B;
    B = x;
  }
  public static int DigitSum(int N)
  {
    string s = N.ToString();
    int ret = 0;
    for (int i = 0; i < s.Length; ++i) ret += s[i] - '0';
    return ret;
  }
}
class Program
{
  static void Main(string[] args)
  {
    var CompetitiveProgramming = new CompetitiveProgramming();
    CompetitiveProgramming.Solve();
  }
}
public static class io
{
  public static string Str => Console.ReadLine();
  public static string[] Strs => Str.Split(' ');
  public static long[] Longs => Strs.Select(long.Parse).ToArray();
  public static int[] Ints => Strs.Select(int.Parse).ToArray();
  public static char[] Chars => Str.ToArray();
  public static double[] Doubles => Strs.Select(double.Parse).ToArray();
  public static long Long1 => Longs[0];
  public static int Int1 => Ints[0];
  public static char Char1 => Chars[0];
  public static double Double1 => Doubles[0];
  public static long[] VerticalRead(int N) { long[] A = new long[N]; for (int i = 0; i < N; ++i) A[i] = Long1; return A; }
  public static void Write(string a) => Console.WriteLine(a);
  public static void Write(params object[] i) => Write(string.Join(" ", i));
  public static void Write<T>(IEnumerable<T> a) => Write(string.Join(" ", a));
  public static void Verticalwrite<T>(IEnumerable<T> a) { foreach (var z in a) Write(z); }
  public static void YN(bool i) { if (i) Write("Yes"); else Write("No"); }
}

Measured memory_bytes: 123684