#include <iostream>
using namespace std;
struct matrice
{
    int lin;
    int col;
};
int a[180][180];
int main()
{
    matrice coada[100*100+2];
    int S=0,i,j,ic=1,sf=1,dirl[4]={1,0},dirc[4]={0,1},lp,cp,linie,coloana,n,m;
    char x;
    cin>>n;
    cin>>m;
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=m;j++)
        {
            cin>>x;
            if(x=='.')
                a[i][j]=0;
            else
                a[i][j]=-1;
        }
    }
    lp=1;
    cp=1;
    for(i=0;i<=n+1;i++)
    {
        a[i][n+1]=-1;
        a[i][0]=-1;
        a[0][i]=-1;
        a[n+1][i]=-1;
    }
    coada[1].lin=lp;
    coada[1].col=cp;
    a[lp][cp]=1;
    while(ic<=sf)
    {
        for(int i=0;i<=1;i++)
        {
                linie=dirl[i]+coada[ic].lin;
                coloana=dirc[i]+coada[ic].col;
                if(a[linie][coloana]==0)
                {
                    sf++;
                    coada[sf].lin=linie;
                    coada[sf].col=coloana;
                    a[linie][coloana]=a[coada[ic].lin][coada[ic].col]+1;
                    if(a[linie][coloana]>S)
                        S=a[linie][coloana];
                }
        }
        ic++;
    }
    cout<<S;
    return 0;
}