#include <bits/stdc++.h>
using namespace std;
int w, h, ans;
char snow[4001][4001];
int check[4001][4001];
queue<pair< pair<int, int>, int> >ord;
int brr=1;
void dfs(int x, int y, int br)
{
//cout<<br<<"\n";
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){ord.push({{x-1, y}, br+1});}
}
else if(snow[x-1][y]=='.')check[x-1][y]=-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){ord.push({{x+1, y}, br+1});}
}
else if(snow[x+1][y]=='.')check[x+1][y]=-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){ord.push({{x, y-1}, br+1});}
}
else if(snow[x][y-1]=='.')check[x][y-1]=-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){ord.push({{x, y+1}, br+1});}
}
else if(snow[x][y+1]=='.')check[x][y+1]=-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];
}
ord.push({{1, 1}, 1});
while(!ord.empty())
{
int xx=ord.front().first.first, yy=ord.front().first.second, bb=ord.front().second;
ord.pop();
if(!check[xx][yy])
{
check[xx][yy]=bb;
dfs(xx, yy, bb);
ans=max(ans, bb);
}
}
//for(int i=1; i<=h; i++){for(int j=1; j<=w; j++)cout<<check[i][j]; cout<<endl;}
cout<<ans;
return 0;
}
