#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int dr[4] = {-1, 0, 1, 0};
int dc[4] = {0, 1, 0, -1};
int n, m;
bool inside(int i, int j)
{
return (i >= 0 && i < n && j >= 0 && j < m);
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
vector<string> a(n);
for (int i = 0; i < n; i++)
{
cin >> a[i];
}
vector<vector<int>> dist(n, vector<int> (m, 0));
deque<pair<int, int>> q;
dist[0][0] = 1;
int ans = 1;
q.push_back({0, 0});
while (!q.empty())
{
auto node = q.front();
q.pop_front();
int i = node.first;
int j = node.second;
int weight = dist[i][j];
ans = max(ans, weight);
for (int k = 0; k < 4; k++)
{
int nr = i + dr[k];
int nc = j + dc[k];
if (inside(nr, nc) && dist[nr][nc] == 0 && a[nr][nc] != '.')
{
int change = (a[i][j] != a[nr][nc]);
dist[nr][nc] = weight + change;
if (change)
{
q.push_back({nr, nc});
}
else
{
q.push_front({nr, nc});
}
}
}
}
cout << ans;
return 0;
}
