#include <bits/stdc++.h>
using namespace std;
#define int long long
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
int n, m;
vector<string> a;
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
void Solve() {
cin >> n >> m;
for(int i = 0; i < n; i++) {
string s;
cin >> s;
a.push_back(s);
}
int dist[n][m];
for(int i = 0; i < n; i++) {
for(int j = 0; j < m; j++) {
dist[i][j] = INT_MAX;
}
}
dist[0][0] = 1;
deque<array<int, 2> > dq;
dq.push_back({0, 0});
int ans = 0;
while(!dq.empty()) {
int curx = dq[0][0], cury = dq[0][1];
ans = max(ans, dist[curx][cury]);
dq.pop_front();
for(int i = 0; i < 4; i++) {
int x = curx + dx[i], y = cury + dy[i];
if(x < 0 || x >= n || y < 0 || y >= m || a[x][y] == '.') {
continue;
}
if(a[x][y] == a[curx][cury] && dist[x][y] > dist[curx][cury]) {
dist[x][y] = dist[curx][cury];
dq.push_front({x, y});
}
if(a[x][y] != a[curx][cury] && dist[x][y] > dist[curx][cury] + 1) {
dist[x][y] = dist[curx][cury] + 1;
dq.push_back({x, y});
}
}
}
cout << ans << "\n";
}
int32_t main() {
auto begin = std::chrono::high_resolution_clock::now();
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
///cin >> t;
while(t--) {
Solve();
}
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n";
return 0;
}
