#include <iostream>
#include <queue>
#include <tuple>
using namespace std;
int H, W;
char grid[4000][4000];
bool visited[4000][4000];
int main() {
cin >> H >> W;
for (int i = 0; i < H; ++i) {
string row;
cin >> row;
for (int j = 0; j < W; ++j) {
grid[i][j] = row[j];
}
}
int answer = 1;
priority_queue<tuple<int, int, int>> queue;
queue.push({-1, 0, 0});
visited[0][0] = true;
while (!queue.empty()) {
auto [marker, i, j] = queue.top();
queue.pop();
answer = max(answer, -marker);
if (i > 0 && !visited[i - 1][j]) {
if (grid[i - 1][j] == grid[i][j]) {
visited[i - 1][j] = true;
queue.push({marker, i - 1, j});
} else if (grid[i - 1][j] != '.') {
visited[i - 1][j] = true;
queue.push({marker - 1, i - 1, j});
}
}
if (i < H - 1 && !visited[i + 1][j]) {
if (grid[i + 1][j] == grid[i][j]) {
visited[i + 1][j] = true;
queue.push({marker, i + 1, j});
} else if (grid[i + 1][j] != '.') {
visited[i + 1][j] = true;
queue.push({marker - 1, i + 1, j});
}
}
if (j > 0 && !visited[i][j - 1]) {
if (grid[i][j - 1] == grid[i][j]) {
visited[i][j - 1] = true;
queue.push({marker, i, j - 1});
} else if (grid[i][j - 1] != '.') {
visited[i][j - 1] = true;
queue.push({marker - 1, i, j - 1});
}
}
if (j < W - 1 && !visited[i][j + 1]) {
if (grid[i][j + 1] == grid[i][j]) {
visited[i][j + 1] = true;
queue.push({marker, i, j + 1});
} else if (grid[i][j + 1] != '.') {
visited[i][j + 1] = true;
queue.push({marker - 1, i, j + 1});
}
}
}
cout << answer << '\n';
}
