//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl '\n'
#define ll long long
#define ull unsigned long long
#define db long double
#define fi first
#define se second
#define pb emplace_back
#define vi vector<int>
#define vii vector<pair<int,int>>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pli pair<ll, int>
#define pdd pair<db, db>
#define iii pair<int, pair<int, int> >
#define ms(s, n) memset(s, n, sizeof(s))
#define all(a) a.begin(), a.end()
#define uni(a) (sort(all(a)), a.resize(unique(all(a))-a.begin()))
#define sz(a) int((a).size())
#define bit(x) bitset<10>((x))
#define MASK(i) (1LL << (i))
#define BIT(x, i) (1 &((x) >> (i)))
#define clz(x) __builtin_clz((x))
#define ctz(x) __builtin_ctz((x))
#define popc(x) __builtin_popcount((x))
#define clzll(x) __builtin_clzll((x))
#define ctzll(x) __builtin_ctzll((x))
#define popcll(x) __builtin_popcountll((x))
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define F0R(i, b) for (int i = 0, _b = (b); i < _b; ++i)
#define FORd(i, a, b) for (int i = (a), _b = (b); i >= _b; --i)
#define F0Rd(i, b) for (int i = (b)-1; i >= 0; i--)
#define rep(i, a) for (auto i : a)
using namespace std;
using namespace __gnu_pbds;
template <typename T>
using ordered_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
void print(int x) {cerr << x;}
void print(long long x) {cerr << x;}
void print(long double x) {cerr << x;}
void print(double x) {cerr << x;}
void print(unsigned long long x) {cerr << x;}
void print(char x) {cerr << x;}
void print(bool x) {cerr << (x ? "True" : "False");}
void print(string x) {cerr << x;}
template <typename T,typename H>
void print(pair<T,H> a) {cerr << "("; print(a.fi); cerr << ','; print(a.se); cerr << ')';}
template <typename T>
void print(T vec) {int cnt=0; cerr << "{"; rep(x,vec) cerr << (cnt++?",":""), print(x); cerr << '}';}
void show() {}
template <typename Head, typename ...Tail>
void show(Head H, Tail ...T){
print(H);
if (sizeof...(T)) cerr << ", ";
show(T...);
}
#define debug(X...) cerr << "LINE " << __LINE__ << " - " << "[" << #X << "] = [", show(X), cerr << "]\n"
template<typename T1,typename T2> bool ckmax(T1 &x,const T2 &y){if(x<y){x=y; return 1;} return 0;}
template<typename T1,typename T2> bool ckmin(T1 &x,const T2 &y){if(y<x){x=y; return 1;} return 0;}
inline int gcd(int x,int y){while(y){int tmp=y;y=x%y;x=tmp;} return (x);}
inline int lcm(int x,int y){return (int)(x*y)/gcd(x,y);}
void read(){}
template <typename Head, typename ...Tail>
void read(Head &H, Tail &...T)
{
int sign = 0;
char c;
for (c = getchar(); !isdigit(c); c = getchar())
if (c == '-') sign = 1;
H = c - '0';
for (c = getchar(); isdigit(c); c = getchar())
H = H * 10 + c - '0';
if (sign) H = -H;
read(T...);
}
mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());
ll rand(ll l, ll r){return l + rd()% (r-l+1);}
const int MOD = 1000000007;
const int mod = 998244353;
const int oo = 1061109567;
const long long INF = 4557430888798830399;
const double PI = acos(-1);
const int N = 4e3 + 1, M = 1e2 + 5;
/*
/\_/\
(= ._.)
/ >? \>$
*/
int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, -1, 1};
int n, m;
int d[N][N];
char a[N][N];
bool check(int x, int y){
if(x < 1 || y < 1) return 0;
if(x > n || y > m) return 0;
if(d[x][y] || a[x][y] == '.') return 0;
return 1;
}
void sol(){
cin >> n >> m;
FOR(i, 1, n) FOR(j, 1, m) cin >> a[i][j];
int ans = 0;
deque<pii> dq; dq.push_back({1, 1});
d[1][1] = 1;
while(sz(dq)){
int x = dq[0].fi;
int y = dq[0].se;
dq.pop_front();
ckmax(ans, d[x][y]);
F0R(i, 4){
int nx = x + dx[i];
int ny = y + dy[i];
if(check(nx, ny)){
if(a[x][y] == a[nx][ny]){
d[nx][ny] = d[x][y];
dq.push_front({nx ,ny});
}
else{
d[nx][ny] = d[x][y] + 1;
dq.push_back({nx ,ny});
}
}
}
}
cout << ans << endl;
// FOR(i, 1, n) FOR(j, 1, m) cout << d[i][j] << " \n"[j == m];
}
signed main(){
#define TASK "nhap"
if(fopen(TASK".inp", "r")){
freopen(TASK".inp", "r", stdin);
freopen(TASK".out", "w", stdout);
}
fast; int t = 1;
// cin >> t;
while(t--) sol();
clog << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << " ms\n";
}
