#include <bits/stdc++.h>
#define FOR(i,x,n) for(int i=x; i<n; i++)
#define F0R(i,n) FOR(i,0,n)
#define ROF(i,x,n) for(int i=n-1; i>=x; i--)
#define R0F(i,n) ROF(i,0,n)
#define WTF cout << "WTF" << endl
#define IOS ios::sync_with_stdio(false); cin.tie(0)
#define F first
#define S second
#define pb push_back
#define ALL(x) x.begin(), x.end()
#define RALL(x) x.rbegin(), x.rend()
using namespace std;
typedef long long LL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef vector<int> VI;
typedef vector<LL> VLL;
typedef vector<PII> VPII;
typedef vector<PLL> VPLL;
const int MAXN = 4000 + 7;
const int ALPHA = 27;
const int INF = 1e9 + 7;
const int MOD = 1e9 + 7;
const int LOG = 22;
int n, m;
int dist[MAXN][MAXN];
char grid[MAXN][MAXN];
deque<PII> keep;
int xm[4] = {1, 0, 0,-1};
int ym[4] = {0,-1, 1, 0};
inline bool safe(int x, int y) {
if (x < 0 || x >= n) return 0;
if (y < 0 || y >= m) return 0;
return 1;
}
int main() {
IOS;
cin >> n >> m;
F0R(i, n) F0R(j, m) cin >> grid[i][j];
F0R(i, n) F0R(j, m) dist[i][j] = INF;
dist[0][0] = 0;
keep.push_front({0, 0});
while(!keep.empty()) {
int x = keep.front().F, y = keep.front().S;
keep.pop_front();
F0R(i, 4) {
int nx = x + xm[i], ny = y + ym[i];
if (safe(nx, ny)) {
if (grid[nx][ny] == '.') continue;
if (grid[nx][ny] == grid[x][y] && dist[nx][ny] > dist[x][y]) {
keep.push_front({nx, ny});
dist[nx][ny] = dist[x][y];
}
if (grid[nx][ny] != grid[x][y] && dist[nx][ny] > dist[x][y] + 1) {
keep.push_back({nx, ny});
dist[nx][ny] = dist[x][y] + 1;
}
}
}
}
int ans = 0;
F0R(i, n) F0R(j, m) if (dist[i][j] != INF) ans = max(ans, dist[i][j]);
cout << ans + 1;
}
