#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define inf 1e17+1
ll const M = 1e5+10;
ll const N = 100001;
const int mod = 1e9+7;
ll dx[8]={1,0,-1,0,1,-1,-1,1};
ll dy[8]={0,1,0,-1,1,-1,1,-1};
ll gcd(ll a, ll b)
{
return b==0 ? a : gcd(b,a%b);
}
int h,w;
string track[4001];
int depth[4001][4001];
int inside(int x,int y)
{
if(x < h and x >= 0 and y < w and y >= 0 and track[x][y] != '.')return true;
return false;
}
void solve(int t) {
// cout << "Case #" << t << ": ";
cin>>h>>w;
for(int i=0;i<h;i++)
{
cin>>track[i];
}
depth[0][0] = 1;
int ans = 1;
deque<pair<int,int>> q;
q.push_back({0,0});
while(!q.empty())
{
pair<int,int> start = q.front();
q.pop_front();
ans = max(ans, depth[start.first][start.second]);
for(int i=0;i<4;i++)
{
int x = start.first + dx[i];
int y = start.second + dy[i];
if(inside(x,y) and depth[x][y]==0)
{
if(track[x][y] == track[start.first][start.second]) {
depth[x][y] = depth[start.first][start.second];
q.push_front({x,y});
}
else
{
depth[x][y] = depth[start.first][start.second] + 1;
q.push_back({x,y});
}
}
}
}
cout<<ans;
}
int main(){
ios_base::sync_with_stdio(false), cin.tie(nullptr);
// #ifndef ONLINE_JUDGE
// freopen("input.txt","r",stdin);
// freopen("output.txt","w",stdout);
// #endif
// int T;
// cin >> T ;
// for(int t = 1; t <= T; t++)
solve(1);
}
