#include <bits/stdc++.h>
using namespace std;
using ll = long long;
vector<int> dr{-1, 1, 0, 0}, dc{0, 0, 1, -1};
const int inf = 1e9;
int main()
{
int n, m;
cin >> n >> m;
vector<vector<char>> a(n, vector<char>(m));
for (int i = 0; i < n; i++)
{
for (int j = 0; j < m; j++)
cin >> a[i][j];
}
deque<pair<int, int>> q;
q.push_back({0, 0});
vector<vector<int>> d(n, vector<int>(m, inf));
d[0][0] = 1;
int ans = 1;
while (!q.empty())
{
auto cur = q.front();
q.pop_front();
int r = cur.first, c = cur.second;
ans = max(ans, d[r][c]);
for (int i = 0; i < 4; i++)
{
int nr = r + dr[i], nc = c + dc[i];
if (nr < 0 || nc < 0 || nr >= n || nc >= m || a[nr][nc] == '.')
continue;
if (d[nr][nc] == inf)
{
if (a[nr][nc] == a[r][c])
{
d[nr][nc] = d[r][c];
q.push_front({nr, nc});
}
else
{
q.push_back({nr, nc});
d[nr][nc] = d[r][c] + 1;
}
}
}
}
cout << ans;
return 0;
}
