#include <bits/stdc++.h>
using namespace std;
int main()
{
cin.tie(0)->sync_with_stdio(0);
int n, m, ans = 1;
cin >> n >> m;
vector <vector <char>> color(n+1, vector <char> (m+1));
vector <vector <int>> depth(n+1, vector <int> (m+1));
for (int i = 1; i <= n; ++i)
for (int j = 1; j <= m; ++j)
cin >> color[i][j];
auto valid = [&](int x, int y, int n, int m, vector <vector <char>>& color) {return x >= 1 && y >= 1 && x <= n && y <= m && color[x][y] != '.';};
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
deque <pair <int, int>> dq;
dq.push_front(make_pair(1, 1));
depth[1][1] = 1;
while (!dq.empty())
{
pair <int, int> cur = dq.front();
dq.pop_front();
ans = max(ans, depth[cur.first][cur.second]);
for (int i = 0; i < 4; ++i)
{
int x = cur.first + dx[i], y = cur.second + dy[i];
if (valid(x, y, n, m, color) && !depth[x][y])
{
if (color[cur.first][cur.second] == color[x][y])
{
depth[x][y] = depth[cur.first][cur.second];
dq.push_front(make_pair(x, y));
} else {
depth[x][y] = depth[cur.first][cur.second] + 1;
dq.push_back(make_pair(x, y));
}
}
}
}
cout << ans << '\n';
}
