#include <cstdio>

using namespace std;


int i,j,m,n,maxx,a[110][110],x;
char ch,s[110];

void fil (int i, int j, int s)
{
    a[i][j] = s;
    if (s>maxx) maxx=s;
    if ((a[i+1][j] != -1) && (s >= a[i+1][j]) && (i<n) && (j<=m)) fil (i+1,j,s+1);
    if ((a[i][j+1] != -1) && (s >= a[i][j+1]) && (i<=n) && (j<m)) fil (i,j+1,s+1);
    return;
}

int main()
{


   scanf ("%d %d",&n,&m);
   for (i=1; i<=n; i++)
   {
       scanf ("%s",s);
       for (j=0; j<m; j++)
       {
           if (s[j]=='.') a[i][j+1] = 0;
            else a[i][j+1] = -1;
       }
   }

   maxx = 0;

   for (i=1; i<=n; i++)
        for (j=1; j<=m; j++)
            if (a[i][j] == 0)
               fil (i,j,1);
    printf ("%d\n",maxx);
    return 0;
}