#include <iostream>
#include <vector>
#include <algorithm>
#include <deque>
using namespace std;
int dx[] = { -1,0,1,0 };
int dy[] = { 0,-1,0,1 };
int main() {
int n, m;
cin >> n >> m;
vector<vector<char>> grid(n + 2, vector<char>(m + 2, '.'));
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> grid[i][j];
}
}
vector<vector<int>> bfs(n + 2, vector<int>(m + 2, 1e9));
bfs[1][1] = 1;
deque<pair<int, int>> cur;
cur.push_back(make_pair(1, 1));
while (cur.size()) {
auto c = cur.front();
cur.pop_front();
for (int i = 0; i < 4; i++) {
int nx = c.first + dx[i];
int ny = c.second + dy[i];
int w = 1;
if (grid[nx][ny] == grid[c.first][c.second]) {
w = 0;
}
if (grid[nx][ny] == '.') {
w = 1e9;
}
if (w != 1e9) {
if (bfs[nx][ny] > bfs[c.first][c.second] + w) {
bfs[nx][ny] = bfs[c.first][c.second] + w;
if (w == 1) {
cur.push_back(make_pair(nx, ny));
}
else {
cur.push_front(make_pair(nx, ny));
}
}
}
}
}
int ans = 1;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (grid[i][j] != '.') {
ans = max(ans, bfs[i][j]);
}
}
}
cout << ans << endl;
}
