#include <iostream>
#include <cassert>
#include <cstring>
#include <queue>
#define ll long long
using namespace std;
const int NMAX = 4000;
const int di[] = { 0, 0, 1, -1 };
const int dj[] = { 1, -1, 0, 0 };
struct Triplet {
int i, j, k;
};
int n, m, answer;
char a[NMAX + 1][NMAX + 1];
char done[NMAX + 1][NMAX + 1];
deque<Triplet> dq;
bool InMat(int i, int j) {
return i >= 1 && i <= n && j >= 1 && j <= m;
}
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> a[i][j];
}
}
dq.push_back({1, 1, 1});
while (!dq.empty()) {
auto [i, j, k] = dq.back();
dq.pop_back();
if (!done[i][j]) {
done[i][j] = 1;
answer = max(answer, k);
for (int d = 0; d < 4; d++) {
int inou = i + di[d];
int jnou = j + dj[d];
if (InMat(inou, jnou) && a[inou][jnou] != '.') {
if (a[inou][jnou] == a[i][j]) {
dq.push_back({ inou, jnou, k });
}
else {
dq.push_front({ inou, jnou, k + 1 });
}
}
}
}
}
cout << answer << '\n';
return 0;
}
