#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define inf __builtin_inf()
constexpr int dy[] = {1, -1, 0, 0};
constexpr int dx[] = {0, 0, 1, -1};
constexpr int N = 4e3 + 5;
char grid[N][N];
bool vis[N][N];
void solve(){
int h, w; cin >> h >> w;
for(int i = 0; i < h; i++){
for(int j = 0; j < w; j++){
cin >> grid[i][j];
}
}
deque<tuple<int, int, int>> q;
q.push_back({1, 0, 0});
int mx = 1;
while(sz(q)) {
const auto [cost, i, j] = q.front();
q.pop_front();
if(vis[i][j]) continue;
vis[i][j] = true;
mx = max(mx, cost);
for(int k = 0; k < 4; k++){
int y = dy[k] + i, x = dx[k] + j;
if(y < 0 || x < 0 || y == h || x == w || vis[y][x] || grid[y][x] == '.') continue;
if(grid[y][x] != grid[i][j]){
q.push_back({cost + 1, y, x});
} else {
q.push_front({cost, y, x});
}
}
}
cout << mx;
}
int main(){
ios_base::sync_with_stdio(false), cin.tie(NULL);
// int t; cin >> t; while(t--)
solve(), cout << '\n';
return 0;
}
