/*-----------------------------
Author : TgX.2
11Ti - K28 - CHV
-----------------------------*/
#include <bits/stdc++.h>
using namespace std;
#ifdef TGX
#include "debug.h"
#else
#define debug(...)
#endif
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; i += 1)
#define FORD(i, a, b) for (int i = (a), _b = (b); i >= _b; i -= 1)
#define fi first
#define se second
#define pb push_back
#define len(x) (int)((x).size())
#define all(x) (x).begin(), (x).end()
#define _ << " " <<
#define __ << "\n"
#define ___ << " "
#define ______________TgX______________ main()
#define int long long
#define intmax 1e9
#define intmin -1e9
#define llongmax 1e18
#define llongmin -1e18
#define memo(a, val) memset((a), (val), sizeof((a)))
struct custom {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
template<class T1, class T2> using cmap = unordered_map<T1, T2, custom>;
template<typename T1, typename T2>
bool mini(T1 &a, T2 b)
{if (a > b) a = b; else return 0; return 1;}
template<typename T1, typename T2>
bool maxi(T1 &a, T2 b)
{if (a < b) a = b; else return 0; return 1;}
/*-----------------------------*/
const int dx[5] = {0, 1, 0, -1};
const int dy[5] = {1, 0, -1, 0};
const int maxn = 4007;
int n, m, dis[maxn][maxn];
char a[maxn][maxn];
void process() {
cin >> n >> m;
FOR(i, 1, n) FOR(j, 1, m)
cin >> a[i][j];
deque<pair<int, int>> q;
q.push_back({1, 1});
int ans = 0;
dis[1][1] = 1;
while(!q.empty()) {
pair<int, int> top = q.front(); q.pop_front();
int x = top.fi, y = top.se;
maxi(ans, dis[x][y]);
FOR(i, 0, 3) {
int xx = x + dx[i];
int yy = y + dy[i];
if (xx < 1 or xx > n or yy < 1 or yy > m or a[xx][yy] == '.') continue;
if (dis[xx][yy] == 0) {
if (a[xx][yy] == a[x][y]) {
dis[xx][yy] = dis[x][y];
q.push_front({xx, yy});
} else {
dis[xx][yy] = dis[x][y] + 1;
q.push_back({xx, yy});
}
}
}
}
cout << ans;
}
/*-----------------------------*/
______________TgX______________ {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
if (fopen("temp.inp", "r")) {
freopen("temp.inp", "r", stdin);
freopen("temp.out", "w", stdout);
}
process();
cerr << "Time: " << 1.0 * clock() / CLOCKS_PER_SEC << " s." __ ;
}
/*==============================+
|INPUT |
--------------------------------|
================================+
|OUTPUT |
--------------------------------|
===============================*/
