#include <bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define ll long long int
#define tc ll test;cin >> test;while(test--)
#define vi vector<ll>
#define pll pair<ll,ll>
#define pb push_back
#define mp make_pair
#define INF 1e18
#define MOD 1e9 + 7
#define ff first
#define ss second
#define in >>
#define out <<
#define space << " " <<
#define spacef << " "
#define fo(i,a,b) for(ll i = a; i <= b; i++)
#define nextline out "\n"
#define print(x) for(auto i : x ) cout out i spacef
#define mmax(x,i) x = max(x,i)
#define mmin(x,i) x = min(x,i)
#define N 105
int main() {
fast;
ll n,m;
cin in n in m;
vector<vector<char>> grid(n+5,vector<char>(m+5,'.'));
fo(i,1,n){
fo(j,1,m){
cin in grid[i][j];
}
}
vector<vi> dist(n+5,vi(m+5,INF));
deque<pll> q;
ll ans = -INF;
vi dx = {-1,1,0,0};
vi dy = {0,0,-1,1};
q.push_front({1,1});
dist[1][1] = 1;
while(!q.empty()){
ll a = q.front().first;
ll b = q.front().second;
q.pop_front();
mmax(ans,dist[a][b]);
fo(t,0,3){
ll aa = a+dx[t];
ll bb = b+dy[t];
if(aa >= 1 && aa <= n && bb >= 1 && bb <= m && grid[aa][bb] != '.'){
if(grid[aa][bb] == grid[a][b] && dist[aa][bb] > dist[a][b]){
dist[aa][bb] = dist[a][b];
q.push_front({aa,bb});
}
else if(grid[aa][bb] != grid[a][b] && dist[aa][bb] > dist[a][b] + 1){
dist[aa][bb] = dist[a][b] + 1;
q.push_back({aa,bb});
}
}
}
}
cout out ans;
return 0;
}
