#include <bits/stdc++.h>
using namespace std;
typedef pair<long long, long long> ll;
const long long INF = 8020;
const long long MAX_h = 4010;
const long long MAX_w = 4010;
char grid[MAX_h][MAX_w];
long long dist[MAX_h][MAX_w];
long long dr[] = {1, -1, 0, 0};
long long dc[] = {0, 0, 1, -1};
int main() {
// freopen("tracksinthesnow_in.txt", "r", stdin);
long long h, w; cin >> h >> w;
for (long long i = 0; i < h; i++) {
for (long long j = 0; j < w; j++) {
cin >> grid[i][j];
}
}
for (long long i = 0; i < h; i++) {
for (long long j = 0; j < w; j++) {
dist[i][j] = INF;
}
}
long long ans = 1;
ll s = ll(0, 0);
deque<ll> q; q.push_front(s); dist[s.first][s.second] = 1;
while (!q.empty()) {
long long r = q.front().first; long long c = q.front().second; q.pop_front();
ans = max(ans, dist[r][c]);
for (long long i = 0; i < 4; i++) {
long long nr = r + dr[i]; long long nc = c + dc[i];
if ((nr < 0 || nr >= h || nc < 0 || nc >= w) || grid[nr][nc] == '.') continue;
if (dist[nr][nc] == INF) {
if (grid[nr][nc] != grid[r][c]) {
dist[nr][nc] = dist[r][c] + 1;
q.push_back(ll(nr, nc));
}
if (grid[nr][nc] == grid[r][c]) {
dist[nr][nc] = dist[r][c];
q.push_front(ll(nr, nc));
}
}
}
}
cout << ans << endl;
return 0;
}
