#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
#include <unordered_map>
#include <unordered_set>
#define ll long long
#define ld long double
#define pl pair<ll, ll>
#define vi vector<ll>
#define vii vector<vi>
#define vc vector<char>
#define vcc vector<vc>
#define vp vector<pl>
#define mi map<ll,ll>
#define mc map<char,int>
#define sortx(X) sort(X.begin(),X.end());
#define all(X) X.begin(),X.end()
#define allr(X) X.rbegin(),X.rend()
#define ln '\n'
#define YES {cout << "YES\n"; return;}
#define NO {cout << "NO\n"; return;}
#define MUN {cout << "-1\n"; return;}
const int MODE = 998244353;
using namespace std;
vp dl = {{0,1}, {0,-1}, {1, 0}, {-1, 0}};
void solve(int tc) {
ll n, m;
cin >> n >> m;
vcc X(n + 10, vc(m + 10, '.'));
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
cin >> X[i+1][j+1];
ll at = 1;
vii ord(n + 10, vi(m + 10));
for (int i = 1; i <= n; i++)
{
for (int j = 1; j <= m; j++)
{
if (X[i][j] == '.' || ord[i][j]) continue;
stack<pl> st;
st.push({i, j});
ord[i][j] = at;
while (!st.empty()) {
auto [l, r] = st.top();
st.pop();
for (auto [x, y] : dl) {
ll a = l + x;
ll b = r + y;
if (!ord[a][b] && X[a][b] == X[i][j]) {
ord[a][b] = at;
st.push({a, b});
}
}
}
at++;
}
}
ll res = 1;
deque<pl> que;
vii vis(n + 10, vi(m + 10, INT32_MAX));
vis[1][1] = 1;
que.push_front({1, 1});
while (!que.empty())
{
pl p = que.front();
que.pop_front();
for (auto [x, y] : dl) {
ll a = x + p.first;
ll b = y + p.second;
ll w = (ord[a][b] != ord[p.first][p.second]);
if (X[a][b] != '.' && vis[a][b] > w + vis[p.first][p.second]) {
vis[a][b] = w + vis[p.first][p.second];
if (w) que.push_back({a,b});
else que.push_front({a,b});
res = max(res, vis[a][b]);
}
}
}
cout << res << '\n';
}
int main()
{
ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
int size = 1;
// freopen("piggyback.in", "r", stdin);
// freopen("piggyback.out", "w", stdout);
// cin >> size;
for (int i = 1; i <= size; i++)
solve(i);
}
