#include <bits/stdc++.h>
#include <deque>
#define ll long long
#define ull unsigned long long
#define pii std::pair<int, int>
#define IO (std::string) ""
std::ifstream fin(IO + ".in");
std::ofstream fout(IO + ".out");
#define NMAX 4001
#define INF INT_MAX
int di[] = {1, -1, 0, 0}, dj[] = {0, 0, 1, -1};
int h, w;
char map[NMAX][NMAX];
void citire() {
std::cin >> h >> w;
for (int i = 0; i < h; i++)
std::cin >> map[i];
}
int dist[NMAX][NMAX];
bool inside(int i, int j) {
return (i > -1 && i < h && j > -1 && j < w && map[i][j] != '.');
}
int bfs01() {
std::deque<pii> q;
q.push_back({0, 0});
dist[0][0] = 1;
int ans = 1;
while (q.size()) {
pii c = q.front();
q.pop_front();
ans = std::max(ans, dist[c.first][c.second]);
for (int i = 0; i < 4; i++) {
int x = c.first + di[i], y = c.second + dj[i];
if (inside(x, y) && dist[x][y] == 0) {
if (map[x][y] == map[c.first][c.second]) {
dist[x][y] = dist[c.first][c.second];
q.push_front({x, y});
} else {
dist[x][y] = dist[c.first][c.second] + 1;
q.push_back({x, y});
}
}
}
}
return ans;
}
int main() {
std::cin.tie(0)->std::ios::sync_with_stdio(0);
citire();
std::cout << bfs01();
return 0;
}
