#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <queue>
#include <map>
#include <utility>
#include <deque>
#include <unordered_map>
using namespace std;
using vi = vector<int>;
typedef long long ll;
typedef unsigned long long ull;
#define pb push_back
const ll MOD = 1e9 + 7;
const ll INF = 1e9;
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};
int depth[4000][4000];
string snow[4000];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n, m;
cin >> n >> m;
for (int i = 0; i < n; i++) {
cin >> snow[i];
}
deque<pair<int ,int>> q;
q.push_back({0, 0});
depth[0][0] = 1;
int ans = 0;
while (!q.empty()) {
auto p = q.front();
int x = p.first, y = p.second;
ans = max(ans, depth[x][y]);
q.pop_front();
for (int i = 0; i < sizeof(dx) / sizeof(dx[0]); i++) {
int nx = x + dx[i], ny = y + dy[i];
if (nx < 0 || nx >= n || ny < 0 || ny >= m || depth[nx][ny] != 0 || snow[nx][ny] == '.') continue;
if (snow[x][y] == snow[nx][ny]) {
depth[nx][ny] = depth[x][y];
q.push_front({nx, ny});
} else {
depth[nx][ny] = depth[x][y] + 1;
q.push_back({nx, ny});
}
}
}
cout << ans << "\n";
return 0;
}
