#include <iostream>
#include <vector>
#include <string>
#include <set>
#include <algorithm>
#include <cstdlib>
#include <random>
#include <stack>
#include <fstream>
#include <iomanip>
#include <unordered_map>
#include <queue>
#include <map>
//#include <popcntintrin.h> // Include the header file for __builtin_popcount
#define ll long long
#define For(i, n) for(ll i = 0; i < n; ++i)
#define ffor(i, a, n) for(ll i = a; i < n; ++i)
#define pb push_back
#define vec vector
#define ff first
#define ss second
#define pairs pair<ll, ll>
#define NEK 1000000000
#define mod 1000000007
using namespace std;
typedef unsigned short int sui;
vec<vec<ll>> d;
ll naj = -1;
struct tr {
ll x, y, w;
};
void BFS(vec<vec<char>>&p) {
deque<tr> q;
d[0][0] = 0;
q.push_back({ 0, 0, 0 });
while (!q.empty()) {
tr x = q.front();
q.pop_front();
for (ll j = -1; j <= 1; j += 2) {
if ((x.x) >= 0 && (x.x) < p.size() && (x.y + j) >= 0 && (x.y + j) < p[0].size()) {
if (p[x.x][x.y + j] == '.') continue;
if (d[x.x][x.y + j] != -1) continue;
if (p[x.x][x.y + j] != p[x.x][x.y]) {
q.push_back({ x.x, x.y + j, x.w + 1 });
d[x.x][x.y + j] = x.w + 1;
naj = max(naj, d[x.x][x.y + j]);
}
else {
q.push_front({ x.x, x.y + j, x.w });
d[x.x][x.y + j] = x.w;
naj = max(naj, d[x.x][x.y + j]);
}
}
}
for (ll i = -1; i <= 1; i += 2) {
if ((x.x + i) >= 0 && (x.x + i) < p.size() && (x.y) >= 0 && (x.y) < p[0].size()) {
if (p[x.x + i][x.y] == '.') continue;
if (d[x.x + i][x.y] != -1) continue;
if (p[x.x + i][x.y] != p[x.x][x.y]) {
q.push_back({ x.x + i, x.y, x.w + 1 });
d[x.x + i][x.y] = x.w + 1;
naj = max(naj, d[x.x + i][x.y]);
}
else {
q.push_front({ x.x + i, x.y, x.w });
d[x.x + i][x.y] = x.w;
naj = max(naj, d[x.x + i][x.y]);
}
}
}
}
return;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
//ifstream cin("subrev.in");
//ofstream cout("subrev.out");
ll h, w;
cin >> h >> w;
vec<vec<char>> p(h, vec<char>(w));
d.resize(h, vec<ll>(w, -1));
For(i, h) {
For(j, w) {
cin >> p[i][j];
}
}
BFS(p);
cout << naj+1 << '\n';
return 0;
}
