#include <iostream>
#include <deque>
using namespace std;
bool check(int x, int y);
int h, w;
string snow[4000];
int main()
{
cin >> h >> w;
for (int i = 0; i < h; i++)
{
cin >> snow[i];
}
deque<pair<int, int>> q;
q.push_back({0, 0});
int depth[h][w];
for (int i = 0; i < h; i++)
{
for (int j = 0; j < w; j++)
{
depth[i][j] = 0;
}
}
depth[0][0] = 1;
int ans = 1;
int dx[] = {-1, 0, 0, 1}, dy[] = {0, -1, 1, 0};
while (!q.empty())
{
pair<int, int> curr = q.front();
q.pop_front();
ans = max(ans, depth[curr.first][curr.second]);
for (int i = 0; i < 4; i++)
{
int x = curr.first + dx[i], y = curr.second + dy[i];
if (depth[x][y] == 0 && check(x, y))
{
if (snow[x][y] == snow[curr.first][curr.second])
{
q.push_front({x, y});
depth[x][y] = depth[curr.first][curr.second];
}
else
{
q.push_back({x, y});
depth[x][y] = depth[curr.first][curr.second] + 1;
}
}
}
}
cout << ans << endl;
return 0;
}
bool check(int x, int y)
{
return x >= 0 && x < h && y >= 0 && y < w && snow[x][y] != '.';
}
