/* IN THE NAME OF GOD */
/* |\/| /-\ |\| | |\/| /-\ */
#include "bits/stdc++.h"
using namespace std;
#define sz(x) (int)x.size()
#define endl '\n'
#define pb push_back
#define all(x) x.begin(), x.end()
#define F first
#define S second
#define mr make_pair
//#define int long long
#define pii pair<int, int>
typedef long double ld;
typedef long long ll;
mt19937 rng (chrono::high_resolution_clock::now().time_since_epoch().count());
const int N = 4e3 + 10;
const int MOD = 1e9 + 7;
const int inf = 1e9 + 1;
int dis[N][N], dx[4] = {0, 0, -1, 1}, dy[4] = {-1, 1, 0, 0};
char c[N][N];
int32_t main(){
ios_base:: sync_with_stdio(0), cin.tie(0), cout.tie(0);
int n, m;
cin >> n >> m;
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m; j++){
cin >> c[i][j];
dis[i][j] = inf;
}
}
deque<pii> q;
q.pb(mr(1, 1));
dis[1][1] = 1;
int ans = 0;
while(!q.empty()){
pii v = q.front();
ans = max(ans, dis[v.F][v.S]);
q.pop_front();
for(int i = 0; i < 4; i++){
if(v.F + dx[i] < 0 || v.F + dx[i] > n || v.S + dy[i] <= 0 || v.S + dy[i] > m)
continue;
if(c[v.F + dx[i]][v.S + dy[i]] == '.')
continue;
bool f = (c[v.F][v.S] == c[v.F + dx[i]][v.S + dy[i]]);
if(f){
if(dis[v.F][v.S] < dis[v.F + dx[i]][v.S + dy[i]]){
dis[v.F + dx[i]][v.S + dy[i]] = dis[v.F][v.S];
q.push_front(mr(v.F + dx[i], v.S + dy[i]));
}
}
else{
if(dis[v.F][v.S] + 1 < dis[v.F + dx[i]][v.S + dy[i]]){
dis[v.F + dx[i]][v.S + dy[i]] = dis[v.F][v.S] + 1;
q.pb(mr(v.F + dx[i], v.S + dy[i]));
}
}
}
}
cout << ans;
}
