#include <bits/stdc++.h>
using namespace std;
bool check(int x, int y, int n, int m, const vector<vector<char>>& snow) {
return (x > -1 && x < n && y > -1 && y < m && snow[x][y] != '.');
}
int main() {
int n, m, res = 1; cin >> n >> m;
vector<vector<char>> snow(n, vector<char> (m));
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) cin >> snow[i][j];
vector<int> dx = {1, 0, -1, 0}, dy = {0, 1, 0, -1};
vector<vector<int>> depth(n, vector<int> (m));
deque<pair<int, int>> q;
q.push_back({0, 0});
depth[0][0] = 1;
while (q.size()) {
pair<int, int> cur = q.front();
q.pop_front();
res = max(res, depth[cur.first][cur.second]);
for (int i = 0; i < 4; i++) {
int x = cur.first + dx[i], y = cur.second + dy[i];
if (check(x, y, n, m, snow) && depth[x][y] == 0) {
if (snow[x][y] == snow[cur.first][cur.second]) {
depth[x][y] = depth[cur.first][cur.second];
q.push_front({x, y});
} else {
depth[x][y] = depth[cur.first][cur.second] + 1;
q.push_back({x, y});
}
}
}
}
cout << res << endl;
}
