#include <bits/stdc++.h>
using namespace std;
int w, h, ans;
char snow[4001][4001];
int check[4001][4001];
void dfs(int x, int y, int br)
{
if(x-1>0)
{
if(snow[x-1][y]==snow[x][y] and check[x-1][y]==0){check[x-1][y]=br; dfs(x-1, y, br);}
else if(snow[x-1][y]!='.')
{
if(check[x-1][y]==0)check[x-1][y]=br+1;
}
}
if(x+1<=h)
{
if(snow[x][y]==snow[x+1][y] and check[x+1][y]==0){check[x+1][y]=br; dfs(x+1, y, br);}
else if(snow[x+1][y]!='.')
{
if(check[x+1][y]==0)check[x+1][y]=br+1;
}
}
if(y-1>0)
{
if(snow[x][y]==snow[x][y-1] and check[x][y-1]==0){check[x][y-1]=br; dfs(x, y-1, br);}
else if(snow[x][y-1]!='.')
{
if(check[x][y-1]==0)check[x][y-1]=br+1;
}
}
if(y+1<=w)
{
if(snow[x][y]==snow[x][y+1] and check[x][y+1]==0){check[x][y+1]=br; dfs(x, y+1, br);}
else if(snow[x][y+1]!='.')
{
if(check[x][y+1]==0)check[x][y+1]=br+1;
}
}
return;
}
int main()
{
cin>>h>>w;
for(int i=1; i<=h; i++)
{
for(int j=1; j<=w; j++)cin>>snow[i][j];
}
check[1][1]=1;
for(int i=1; i<=h; i++)
{
for(int j=1; j<=w; j++)
{
if(snow[i][j]=='.')check[i][j]=-1;
else {dfs(i, j, check[i][j]); ans=max(ans, check[i][j]);}
}
}
cout<<ans;
return 0;
}
