#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <cstdlib>
using namespace std;
const int maxn = 1001;

bool v[maxn][maxn];

int ans = 0;

int findlongest(int i ,int j )
{
    if(v[i][j]==0)return 0;
    v[i][j]=0;
    int maxans = 0;
    vector<int> vv;
    int temp;
    if(v[i-1][j])
    {
        temp = findlongest(i-1, j);
        if(temp!=0)vv.push_back(temp);
    }
    if(v[i][j-1])
    {
        temp = findlongest(i, j-1);
        if(temp!=0)vv.push_back(temp);
    }
    if(v[i+1][j])
    {
        temp = findlongest(i+1, j);
        if(temp!=0)vv.push_back(temp);
    }
    if(v[i][j+1])
    {
        temp = findlongest(i, j+1);
        if(temp!=0)vv.push_back(temp);
    }
    sort(vv.begin(),vv.end());
    for( int k = vv.size()-1;k>=0 && vv.size()-k>=2;k--)
        maxans+=vv[k];
    ans=max(ans,maxans+1);
    if(!vv.size())return 1;
    return vv[vv.size()-1]+1;
}
#define get(i) scanf("%c",&i);

int main()
{
    freopen("input.txt", "r", stdin);
    freopen("output.txt","w",stdout);
       // memset(v,false,sizeof(v));
        int i,j;
        char c;
        int n ,m;
    cin>>n>>m;
        int k , t;
        for(i = 0 ;i<m;i++)
            for(j = 0;j<n;j++)
            {
                cin>>c;
                if(c == '.')v[i][j]=true;
            }

        for(j = 0;j<n;j++)
            for(i = 0 ;i<m;i++)
                if(v[i][j]){k = i;t = j;break;}

        ans = max(ans,findlongest(k,t));
        cout<<ans-1<<endl;
    return 0;
}