#include <vector>
#include <iostream>
#include <cassert>
#include <cmath>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <algorithm>
#include <iomanip>
using namespace std;
vector<vector<bool>> hasVisited;
vector<string> grid;
vector<pair<int, int>> pos = {{0, 1},
{-1, 0},
{0, -1},
{1, 0}};
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n, m;
cin >> n >> m;
deque<pair<int, pair<int, int>>> q;
grid.resize(n), hasVisited.resize(n);
for (int i = 0; i < n; i++) {
cin >> grid[i];
hasVisited[i].assign(m, false);
}
q.push_back({1, {0, 0}});
int myMax = 0;
while (!q.empty()) {
pair<int, int> loc = q.front().second;
int dist = q.front().first;
q.pop_front();
if (hasVisited[loc.first][loc.second]) {
continue;
}
myMax = max(myMax, dist);
hasVisited[loc.first][loc.second] = true;
for (auto p: pos) {
int nx = loc.first + p.first;
int ny = loc.second + p.second;
if (nx >= 0 && ny >= 0 && nx < n && ny < m && grid[nx][ny] != '.') {
if (grid[nx][ny] != grid[loc.first][loc.second]) {
q.push_back(make_pair(dist + 1, make_pair(nx, ny)));
} else {
q.push_front(make_pair(dist, make_pair(nx, ny)));
}
}
}
}
cout << myMax;
}
