#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define FOR(i,a,b) for(__typeof(b) i=a; i<=b; i++)
#define FOD(i,a,b) for(__typeof(b) i=b; i>=a; i--)
#define EACH(u, v) for(auto& u : v)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define pf push_front
#define ii pair<int,int>
#define iii pair<int,ii>
#define f first
#define s second
#define ed "\n"
#define sp " "
#define vi vector<int>
#define vii vector<ii>
#define vl vector<ll>
#define NO cout << "NO" << ed;
#define YES cout << "YES" << ed;
#define no cout << "no" << ed;
#define yes cout << "yes" << ed;
void setIO(string fileName = ""){
if(fileName.length()){
freopen((fileName+".in").c_str(), "r", stdin);
freopen((fileName+".out").c_str(), "w", stdout);
}
}
const int oo1 = 1e9 + 7;
const int oo2 = 1e9 + 9;
const int d4x[] = {0, 0, 1, -1};
const int d4y[] = {1, -1, 0, 0};
const int d8x[] = {-1, 0, 1, -1, 1, -1, 0, 1};
const int d8y[] = {1, 1, 1, 0, 0, -1, -1, -1};
const int N = 4000 + 10;
const int M = 1e2 + 10;
vi adj[N];
int n, m, dep[N][N];
char a[N][N];
bool ok(int x, int y)
{
return x && y && x <= n && y <= m && a[x][y] != '.';
}
void solve()
{
cin >> n >> m;
FOR(i, 1, n) FOR(j, 1, m) cin >> a[i][j];
int ans = 0;
deque<ii> q;
q.pb({1, 1});
dep[1][1] = 1;
while(sz(q)) {
ii cur = q.front();
q.pop_front();
ans = max(ans, dep[cur.f][cur.s]);
FOR(i, 0, 3) {
int x = cur.f + d4x[i];
int y = cur.s + d4y[i];
if(ok(x, y) && !dep[x][y]) {
if(a[x][y] == a[cur.f][cur.s]) {
dep[x][y] = dep[cur.f][cur.s];
q.pf({x, y});
} else {
dep[x][y] = dep[cur.f][cur.s] + 1;
q.pb({x, y});
}
}
}
}
cout << ans;
}
int main()
{
ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
setIO("");
int t; t = 1;
//int t; cin >> t;
FOR(i, 1, t) {
solve();
}
return 0;
}
