#include <iostream>
#include <string>
#include <deque>
using namespace std;
int h, w;
int depth[4000][4000];
int ans = 1;
string snow[4000];
bool inside(int x, int y)
{
return (x > -1 && x < h && y > -1 && y < w && snow[x][y] != '.');
}
int main ()
{
cin >> h >> w;
for (int i = 0; i < h; i++)
{
cin >> snow[i];
}
for(int i = 0; i < h; i++)
{
for(int j = 0; j < w; j++)
{
depth[i][j] = 0;
}
}
deque<pair<int, int>> q;
q.push_front({0, 0});
depth[0][0] = 1;
int dx[4], dy[4];
dx[0] = 1; dx[1] = -1; dx[2] = 0; dx[3] = 0;
dy[0] = 0; dy[1] = 0; dy[2] = 1; dy[3] = -1;
while(!q.empty())
{
pair<int, int> c = q.front();
q.pop_back();
ans = max(ans, depth[c.first][c.second]);
for (int i = 0; i < 4; i++)
{
int x = c.first + dx[i], y = c.second + dy[i];
if (inside(x, y) && depth[x][y] == 0)
{
if (snow[x][y] == snow[c.first][c.second])
{
depth[x][y] = depth[c.first][c.second];
q.push_front({x, y});
}
else
{
depth[x][y] = depth[c.first][c.second] + 1;
q.push_back({x, y});
}
}
}
}
cout << ans;
}
