#include<bits/stdc++.h>
// #define int ll
#define forn(i,n) for(int i=0;i<(n);i++)
#define Forn(i,n) for(int i=1;i<=(n);i++)
#define For(i, a, b) for (int i = a; i <= b; i++)
#define foR(i, a, b) for (int i = a; i >= b; i--)
#define ll long long
#define pb push_back
#define F first
#define S second
#define lb lower_bound
#define ub upper_bound
#define vi vector<int>
#define vl vector<long long>
#define vpi vector<pair<int,int> >
#define pii pair<int,int>
#define pll pair<long long,long long>
#define mp make_pair
#define all(p) p.begin(),p.end()
#define alr(p,q) p+1,p+q+1
#define ull unsigned long long
#define st0(p) memset((p),0,sizeof(p))
#define T(x) ((x)%2 ? s[(x)/2] : '.')
#define lowb(x) x&-x
#define sz(x) (x).size()
#define rz resize
#define printv(x) {for(auto &i : x) {cout << i << ' ';}cout <<'\n';}
using namespace std;
inline void USACO(string filename){
freopen((filename+".in").c_str(),"r",stdin);
freopen((filename+".out").c_str(),"w",stdout);
}
void debug() {cout << endl;}
template <class T, class ...U> void debug(T a, U ... b) { cout << a << " "; debug(b...);}
// template <class T> int max(T a, T ... b) { cout << a << " "; debug(b...);}
const int INF = 1e9+7;
const int mod = 1e9+7;
const int N = 4e3+9;
const int C = 35;
const double eps = 1e-7;
int n,m;
int d[N][N];
char c[N][N];
int dx[4] = {1,0,-1,0};
int dy[4] = {0,1,0,-1};
bool vis[N][N];
bool inside(int x,int y){
return !(x < 0 || y < 0 || x >= n || y >= m || c[x][y] == '.');
}
void solve(){
cin >> n >> m;
forn(i,n) forn(j,m) cin >> c[i][j];
deque<pii> dq;
dq.pb({0,0});
int ans = 0;
while(!dq.empty()){
pii cur = dq.front();dq.pop_front();
vis[cur.F][cur.S] = 1;
forn(i,4){
int nx = cur.F + dx[i],ny = cur.S + dy[i];
if(inside(nx,ny) && !vis[nx][ny] ){
// debug(nx,ny);
if(c[nx][ny] == c[cur.F][cur.S]) {
d[nx][ny] = d[cur.F][cur.S];
dq.push_front({nx,ny});
}else{
d[nx][ny] = d[cur.F][cur.S] +1;
dq.push_back({nx,ny});
}
}
}
ans = max(ans,d[cur.F][cur.S]);
}
cout << ans+1 << '\n';
}
signed main(){
// USACO("248");
cin.tie(0);
cout.tie(0);
ios_base::sync_with_stdio(0);
// cout << "?";
// cout << fixed << setprecision(15);
solve();
return 0;
}
