#include <bits/stdc++.h>
using namespace std;
#define int long long
vector<pair<int,int>> dirs = {{0,1},{1,0},{-1,0},{0,-1}};
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<vector<char>> v(n,vector<char>(m));
for(int i = 0; i < n; ++i) {
for(int j = 0; j < m; ++j) cin >> v[i][j];
}
vector<vector<int>> dist(n,vector<int>(m,-1));
deque<tuple<int,int,int>> q;
q.push_front({0,0,0});
while(!q.empty()) {
const auto [i,j,w] = q.front();
q.pop_front();
dist[i][j] = w;
for(const auto& [a,b] : dirs) {
int ni = a + i, nj = j + b;
if(ni < 0 || nj < 0 || ni >= n || nj >= m || dist[ni][nj] != -1 || v[ni][nj] == '.') continue;
if(v[ni][nj] != v[i][j]) {
q.push_back({ni,nj,w+1});
}
else {
q.push_front({ni,nj,w});
}
}
}
int ans = -1;
for(const vector<int>& i : dist) for(int j : i) ans = max(ans,j);
cout<<ans+1<<endl;
}
