#include<bits/stdc++.h>
#define ll long long
#define task ""
using namespace std;
const int maxn = 4005;
int m, n, di[4] = {0, 0, 1, -1}, dj[4] = {1, -1, 0, 0}, sz[maxn][maxn], d[maxn][maxn], res = 0;
pair<int, int> par[maxn][maxn];
vector<pair<int, int>> adj[maxn][maxn];
char c[maxn][maxn];
deque<pair<int, int>> dq;
int main()
{
//freopen(task".INP", "r", stdin);
//freopen(task".OUT", "w", stdout);
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
memset(d, -1, sizeof(d));
cin >> m >> n;
for (int i = 1; i <= m; i++)
for (int j = 1; j <= n; j++)
{
cin >> c[i][j];
sz[i][j] = 1;
}
for (int i = 1; i <= m; i++)
for (int j = 1; j <= n; j++)
{
if (c[i][j] == '.') continue;
if (par[i][j].first != 0) continue;
par[i][j] = {i, j};
dq.push_back({i, j});
while (!dq.empty())
{
int i = dq.front().first, j = dq.front().second;
dq.pop_front();
for (int d = 0; d < 4; d++)
{
int ni = i + di[d], nj = j + dj[d];
if (ni < 1 || ni > m || nj < 1 || nj > n) continue;
if (c[i][j] == c[ni][nj] && par[ni][nj].first == 0)
{
par[ni][nj] = par[i][j];
dq.push_back({ni, nj});
}
}
}
}
for (int i = 1; i <= m; i++)
for (int j = 1; j <= n; j++)
{
if (c[i][j] == '.') continue;
for (int d = 0; d < 4; d++)
{
int ni = i + di[d], nj = j + dj[d];
if (ni < 1 || ni > m || nj < 1 || nj > n) continue;
if (c[ni][nj] == '.') continue;
if (c[i][j] != c[ni][nj])
{
adj[par[i][j].first][par[i][j].second].push_back(par[ni][nj]);
adj[par[ni][nj].first][par[ni][nj].second].push_back(par[i][j]);
}
}
}
dq.push_back(par[m][n]);
d[par[m][n].first][par[m][n].second] = 1;
res = 1;
while (!dq.empty())
{
int x = dq.front().first, y = dq.front().second;
dq.pop_front();
for (pair<int, int> p : adj[x][y])
if (d[p.first][p.second] == -1)
{
d[p.first][p.second] = d[x][y] + 1;
res = max(res, d[p.first][p.second]);
dq.push_back(p);
}
}
cout << res;
}
