#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll MAX = 4001, MOD = 1000000007;
ll t = 1, n, m, nx, ny, mx;
vector<string> v(MAX);
vector dist(MAX,vector<ll>(MAX, 1e9));
vector<pair<int, int>> adj = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
//freopen("checklist.in", "r", stdin);
//freopen("checklist.out", "w", stdout);
//cin >>t;
while(t--) {
cin >> n >> m;
for (int i = 0; i < n; i++) cin >> v[i];
deque<pair<int, int>>q;
q.push_front({0, 0});
dist[0][0]=1;
while(!q.empty()) {
auto[x, y] = q.front();
q.pop_front();
//cout << x << " " << y << endl;
for (auto[cx, cy]:adj) {
nx = x+cx;
ny = y+cy;
if (nx<0||ny<0||nx>=n||ny>=m||v[nx][ny]=='.')continue;
if (v[nx][ny]==v[x][y]&&dist[nx][ny]>dist[x][y]) {
dist[nx][ny]=dist[x][y];
q.push_front({nx, ny});
}else if (v[nx][ny]!=v[x][y]&&dist[nx][ny]>dist[x][y]+1){
dist[nx][ny]=dist[x][y]+1;
q.push_back({nx, ny});
}
}
}
mx = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
//cout << (dist[i][j]==1e9?0:dist[i][j])<< " ";
if (dist[i][j]==1e9)continue;
mx = max(mx, dist[i][j]);
}
//cout << endl;
}
cout << mx << endl;
}
//fclose(stdin);
//fclose(stdout);
return 0;
}
