/*
* Author : recedivies
* Problem Link : https://tlx.toki.id/problems/osn-2017/2B/
* Mei 20, 2021
*/
#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef string str;
#define io() ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define PB push_back
#define MP make_pair
#define F first
#define S second
#define sz(a) ((int)(a).size())
#define mset(a, b) memset(a, b, sizeof(a))
#define print(a, n) for(int _i = 0 ; _i < n ; _i++) cout << a[_i] << " "; cout << '\n';
#define print2(a, n, m) for(int _i = 0 ; _i < n ; _i++){for(int _j = 0 ; _j < m ; _j++){cout << a[_i][_j] << " ";} cout << '\n';}
int dd[123];
ll Read() {
char ch = getchar();
while (ch < '0' || ch > '9') {
ch = getchar();
}
ll v = 0;
while ('0' <= ch && ch <= '9') {
v = v * 10 + (int) (ch - '0');
ch = getchar();
}
return v;
}
void Write(ll x) {
int len = 0;
while (x > 0) {
dd[len++] = x % 10;
x /= 10;
}
for (int i = len - 1; i >= 0; i--) {
putchar('0' + dd[i]);
}
if (len == 0) {
putchar('0');
}
putchar(' ');
}
template < typename F, typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
return os << "(" << p.first << ", " << p.second << ")";
}
template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
os << "{";
for (auto it = v.begin(); it != v.end(); ++it)
{
if ( it != v.begin() )
os << ", ";
os << *it;
}
return os << "}";
}
template < typename T >
ostream &operator << ( ostream & os, const set< T > &v ) {
os << "[";
for (auto it = v.begin(); it != v.end(); ++it)
{
if ( it != v.begin())
os << ", ";
os << *it;
}
return os << "]";
}
template < typename F, typename S >
ostream &operator << ( ostream & os, const map< F, S > &v ) {
os << "[";
for (auto it = v.begin(); it != v.end(); ++it)
{
if ( it != v.begin() )
os << ", ";
os << it -> first << " = " << it -> second ;
}
return os << "]\n";
}
#define deb(args...) do {cerr << #args << " = "; faltu(args); } while(0)
#define debug(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#define time(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false); debug("%s Time : %.4fs", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))
void faltu () {
cerr << endl;
}
template <typename T>
void faltu( T a[], int n ) {
for (int i = 0; i < n; ++i)
cerr << a[i] << ' ';
cerr << endl;
}
template <typename T, typename ... hello>
void faltu( T arg, const hello &... rest) {
cerr << arg << ' ';
faltu(rest...);
}
template <class T> T egcd(T a , T b , T &x , T &y){T gcd , xt , yt;if(a == 0){gcd = b;x = 0 , y = 1;}else {gcd = egcd(b % a , a , xt , yt);x = yt - (b/a)*xt; y = xt;}return gcd;}
template <class T> T expo(T base , T exp , T mod){T res = 1;base = base % mod;while (exp > 0){if (exp & 1)res = (res*base) % mod;exp = exp>>1;base = (base*base) % mod;}return res;}
template <class T> T modinv(T a , T mod){T x , y; egcd<T>(a , mod , x , y);while(x < 0) x += mod; while(x >= mod) x -= mod; return x;}
template <class T> T modinvfermat(T a , T mod){return expo<T>(a , mod - 2 , mod);}
template <class T> bool rev(T a , T b){return a > b;}
template <class T> ll maxpower(T a , T b){ll ans = 0;while(a > 0 && a % b == 0){ans++;a /= b;}return ans;}
template <class T> T mceil(T a, T b){if(a % b == 0) return a/b; else return a/b + 1;}
template <class T> T lcm(T a, T b){return (a)/__gcd<T>(a, b)*(b);}
//const int MOD = (119 << 23) + 1;
const int MOD = 1e9 + 7;
const ll INF = (ll) 1e18;
const double PI = acos(-1);
const double EPS = 1e-9;
const int MAX = 2e9;
const int dx[4] = {+1, 0, -1, 0};
const int dy[4] = {0, +1, 0, -1};
//const int dx[8] = {+1, +1, -1, -1, 0, 0, +1, -1};
//const int dy[8] = {+1, -1, -1, +1, +1, -1, 0, 0};
const int N = 4001;
char a[N][N];
int dist[N][N];
int n, m;
bool isValid(int i, int j) {
return i >= 0 && j >= 0 && i < n && j < m;
}
int main() {
io();
cin >> n >> m;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
dist[i][j] = MAX;
cin >> a[i][j];
}
}
deque<pair<int, int>> q;
q.push_front({0, 0});
dist[0][0] = 0;
while (!q.empty()) {
int u = q.front().first, v = q.front().second;
q.pop_front();
for (int k = 0; k < 4; k++) {
int r = dx[k] + u;
int c = dy[k] + v;
if (isValid(r, c) && a[r][c] != '.' && dist[r][c] > dist[u][v] + 1) {
if (a[r][c] == a[u][v]) {
dist[r][c] = dist[u][v];
q.push_front({r, c});
} else {
dist[r][c] = dist[u][v] + 1;
q.push_back({r, c});
}
}
}
}
int ans = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (dist[i][j] != MAX) ans = max(ans, dist[i][j] + 1);
}
}
cout << ans << '\n';
return 0;
}
/*
5 8
FFR.....
.FRRF...
.RRFFFFF
..RRRFFR
.....FFF
*/
