#include "bits/stdc++.h"
using namespace std;
using ll = long long;
using pii = pair < int, int >;
using pll = pair < ll, ll >;
template<class T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }
#define FOR(i, a, b) for(int i = a; i <= b; i++)
#define FORD(i, a, b) for(int i = a; i >= b; i--)
#define REP(i, b) for(int i = 0; i < b; i++)
#define PER(i, b) for(int i = b - 1; i >= 0; i--)
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#define debugArr(...) 42
#endif
const int INF = 1e9;
const int MOD = 1e9 + 7;
const int MAX = 4005;
int n, m;
char a[MAX][MAX];
int dx[] = {0, 1, 0, -1};
int dy[] = {-1, 0, 1, 0};
int d[MAX][MAX];
bool isInside(int x, int y){
return (1 <= x && x <= n && 1 <= y && y <= m && a[x][y] != '.');
}
void run_case(){
cin >> n >> m;
FOR(i, 1, n) FOR(j, 1, m) cin >> a[i][j];
int ans = 1;
deque<pii> q;
q.push_front({1, 1});
d[1][1] = 1;
while (!q.empty()){
auto [x, y] = q.front();
q.pop_front();
ckmax(ans, d[x][y]);
REP(i, 4){
int nx = x + dx[i];
int ny = y + dy[i];
if (isInside(nx, ny) && d[nx][ny] == 0){
if (a[x][y] == a[nx][ny]){
d[nx][ny] = d[x][y];
q.push_front({nx, ny});
}
else {
d[nx][ny] = d[x][y] + 1;
q.push_back({nx, ny});
}
}
}
}
cout << ans << "\n";
}
signed main(){
cin.tie(0) -> sync_with_stdio(0);
int Test = 1;
//cin >> Test;
FOR(i, 1, Test){
run_case();
}
}
// Codename : Jasper the Otter
