#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
// #define int long long
#define pii pair<ll, ll>
#define fi first
#define se second
const ll N = 2e5 + 5, inf = 1e9, mod = 1e9 + 7, block = 320;
int n, m;
vector <vector <char> > a;
vector <vector <int> > length;
struct item {
int x, y, val;
bool operator <(const item &other) const {
return val > other.val;
}
};
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};
void dijk() {
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
length[i][j] = inf;
}
}
length[1][1] = 1;
priority_queue <item> q;
q.push({1, 1, 1});
while(q.size()) {
auto [x, y, val] = q.top();
q.pop();
if (val > length[x][y]) continue;
for (int i = 0; i < 4; i++) {
int nx = x + dx[i];
int ny = y + dy[i];
if (nx > n || nx < 1 || ny > m || ny < 1 || a[nx][ny] == '.') continue;
if (a[x][y] == a[nx][ny] && length[nx][ny] > length[x][y]) {
length[nx][ny] = length[x][y];
q.push({nx, ny, length[nx][ny]});
}
if (a[x][y] != a[nx][ny] && length[nx][ny] > length[x][y] + 1) {
length[nx][ny] = length[x][y] + 1;
q.push({nx, ny, length[nx][ny]});
}
}
}
int ans = 0;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (length[i][j] < inf) ans = max(ans, length[i][j]);
}
}
cout << ans;
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(0);
cin >> n >> m;
a.assign(n + 1, vector <char> (m + 1, 0));
length.assign(n + 1, vector <int> (m + 1, 0));
for (int i = 1; i <= n; i++) {
string s;
cin >> s;
for (int j = 1; j <= m; j++) {
a[i][j] = s[j - 1];
}
}
dijk();
return 0;
}
