#include<bits/stdc++.h>
#define a first
#define b second
using namespace std;
typedef pair<int, int>PII;
const int MAXL = 4000;
int n, m;
vector<string>graph;
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
int main()
{
int ans = 1; // 至少有一个animal
iostream :: sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
graph.resize(n);
for(int i = 0; i < n; i ++)
cin >> graph[i];
// 0-1 bfs 0 -> push_front, 1 -> push_back() --> increasing deque
// q 存储位置
// dist 存储到 start 的距离
deque<PII>q;
q.push_back({0, 0});
vector<vector<int>>dist(n, vector<int>(m, INT_MAX));
dist[0][0] = 1; // 根的depth是1
while(q.size())
{
auto t = q.front();
q.pop_front();
ans = max(ans, dist[t.a][t.b]);//已可用它更新其它点的dist是否最大
// 字母走方向的图不是adj的图
for(int i = 0; i < 4; i ++)
{
int x = t.a + dx[i], y = t.b + dy[i];
if(x < 0 || x >= n || y < 0 || y >= m)continue;
if((graph[x][y] == '.' ) || dist[x][y] != INT_MAX)continue;// un-visited
// 在同一node内，weight为0
if(graph[x][y] == graph[t.a][t.b])
{
q.push_front({x, y});
dist[x][y] = dist[t.a][t.b];
}
else
{
q.push_back({x, y});
dist[x][y] = dist[t.a][t.b] + 1;
}
}
}
cout << ans << endl;
return 0;
}
