#include <bits/stdc++.h>
#pragma GCC optimize ("O4")
#pragma GCC optimize ("fast-math")
#pragma GCC optimize ("unroll-loops")
using namespace std;
#define int long long
#define ll long long
#define XX first
#define YY second
#define all (x) begin(x), end(x)
/**
#define cin fin
#define cout fout
ifstream cin ("pfn.in");
ofstream cout ("pfn.out");
**/
typedef double dbl;
typedef long double ldb;
typedef pair <int, int> pii;
typedef vector <int> vii;
typedef pair <double, int> pdi;
const int SMAX = 10;
const int VMAX = 1;
const int RMAX = 179;
const int NMAX = 4e3;
int n, m;
char v[NMAX + 1][NMAX + 1];
int matrix[NMAX + 1][NMAX + 1];
struct elem {
int x, y;
};
void read(){
cin >> n >> m;
for (int i = 1; i <= n; ++ i){
for (int j = 1; j <= m; ++ j){
cin >> v[i][j];
}
}
}
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
bool outmat (const elem &a){
return a.x < 1 || a.x > n || a.y < 1 || a.y > m;
}
void solve (){
int maxi = 1;
matrix[1][1] = 1;
deque <elem> pq;
pq.push_front({1, 1});
while (!pq.empty()){
elem val = pq.front();
pq.pop_front();
maxi = max (maxi, matrix[val.x][val.y]);
for (int i = 0; i < 4; ++ i){
elem s = {val.x + dx[i], val.y + dy[i]};
if (!outmat(s) && matrix[s.x][s.y] == 0 && v[s.x][s.y] != '.'){
if (v[s.x][s.y] == v[val.x][val.y])
{
matrix[s.x][s.y] = matrix[val.x][val.y];
pq.push_front(s);
}
else
{
matrix[s.x][s.y] = matrix[val.x][val.y] + 1;
pq.push_back(s);
}
}
}
}
cout << maxi;
}
signed main(void){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int query = 1;
while (query --){
read();
solve();
}
return 0 ^ 0;
}
