#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ii = pair<int, int>;
using vi = vector<int>;
using db = double;
#define ff first
#define ss second
#define pb push_back
#define all(x) x.begin(), x.end()
#define lb lower_bound
#define ub upper_bound
const int nx[4] = {0, 0, 1, -1}, ny[4] = {1, -1, 0, 0};
int n, m, dis[4005][4005];
char grid[4005][4005];
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for(int l = 0; l < n; l++)
for(int i = 0; i < m; i++)
cin >> grid[l][i];
dis[0][0] = 1; int res = 1;
deque<ii> q; q.push_front({0, 0});
while(!q.empty()) {
ii a = q.front(); res = max(res, dis[a.ff][a.ss]); q.pop_front();
for(int l = 0; l < 4; l++) {
int x = a.ff + nx[l], y = a.ss + ny[l];
if(x >= 0 && x < n && y >= 0 && y < m && grid[x][y] != '.' && dis[x][y] == 0) {
if(grid[x][y] == grid[a.ff][a.ss]) {
dis[x][y] = dis[a.ff][a.ss];
q.push_front({x, y});
}
else {
dis[x][y] = dis[a.ff][a.ss] + 1;
q.push_back({x, y});
}
}
}
}
cout << res << "\n";
}
