#include <bits/stdc++.h>
using namespace std;
int xdir[4] = {0,0,1,-1};
int ydir[4] = {1,-1,0,0};
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>> dis(n,vector<int>(m,-1));
deque<pair<int,int>> myq;
myq.push_front({0,0});
dis[0][0] = 0;
int ans = 0;
while (!myq.empty())
{
pair<int,int> u = myq.front();
myq.pop_front();
ans = max(ans, dis[u.first][u.second]);
for (int i = 0; i < 4; i++)
{
int x = u.first + xdir[i];
int y = u.second + ydir[i];
if (x < 0 || x == n || y < 0 || y == m || dis[x][y] != -1 || grid[x][y] == '.') continue;
if (grid[x][y] == grid[u.first][u.second])
{
dis[x][y] = dis[u.first][u.second];
myq.push_front({x,y});
}
else
{
dis[x][y] = dis[u.first][u.second] + 1;
myq.push_back({x,y});
}
}
}
cout << ans << '\n';
return 0;
}
