#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
#define pb push_back
#define F first
#define S second
#define ii pair<ll,ll>
const long double eps=1e-16;
const ll N = 3e5 + 5, M = 3e5 + 50, LOG = 21, mod = 1000000007, INF = 1e18;
const ld EPS = 1e-16;
ll n,m;
vector<int> adj[N];
int dis[500][500];
string s[500];
bool valid(int i,int j){
return i>=0 && i<n && j>=0 &&j <m && s[i][j]!='.';
}
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};
int main() {
// ios_base::sync_with_stdio(0); cin.tie(0);cout.tie(0);
ll tt = 1;
// cin >>tt;
while (tt--) {
cin >>n >>m;
for (int i = 0; i < n; ++i) {
cin >>s[i];
}
deque<pair<int,int>>dq;
dq.push_back({0,0});
dis[0][0]=1;
int ans=0;
while (!dq.empty()){
auto cur=dq.front();
dq.pop_front();
ans=max(ans,dis[cur.first][cur.second]);
for (int i = 0; i < 4; ++i) {
int x=cur.first+dx[i],y=cur.second+dy[i];
if(valid(x,y) && dis[x][y]==0){
if(s[x][y]==s[cur.first][cur.second]){
dis[x][y]=dis[cur.first][cur.second];
dq.push_front({x,y});
}else{
dis[x][y]=dis[cur.first][cur.second]+1;
dq.push_back({x,y});
}
}
}
}
cout << ans <<endl;
}
}
