#include <bits/stdc++.h>
using namespace std;
int main()
{
int n, m;
cin >> n >> m;
vector<vector<char>> grid(n, vector<char> (m));
for(int i = 0; i < n; i++)
{
for(int j = 0; j < m; j++)
{
cin >> grid[i][j];
}
}
vector<vector<int>> distances(n, vector<int> (m));
vector<int> dir_x = {1, -1, 0, 0}, dir_y = {0, 0, 1, -1};
deque<pair<int, int>> q;
q.push_front({0, 0});
distances[0][0] = 1;
int ans = 0;
while(q.size())
{
auto src = q.front();
q.pop_front();
for(int i = 0; i < 4; i++)
{
int x = src.first + dir_x[i], y = src.second + dir_y[i];
if(x >= 0 && x < n && y >= 0 && y < m && grid[x][y] != '.' && distances[x][y] == 0)
{
if(grid[x][y] == grid[src.first][src.second])
{
distances[x][y] = distances[src.first][src.second];
q.push_front({x, y});
}
else
{
distances[x][y] = distances[src.first][src.second] + 1;
q.push_back({x, y});
}
ans = max(ans, distances[x][y]);
}
}
}
cout << ans << endl;
return 0;
}
