//#pragma GCC target("avx2")
//#pragma GCC optimization("O3")
//#pragma GCC optimization("unroll-loops")
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define ff first
#define ss second
#define pb push_back
#define SZ(x) ((int)(x).size())
#define all(x) x.begin(), x.end()
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define Re(i, a, b) for(int i = (a); i >= (b); i--)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int H, W;
vector<vector<char>> a;
int dx[] = {-1, +1, 0, 0};
int dy[] = {0, 0, -1, +1};
bool valid(int x, int y){
return (x >= 0 && x < H && y >= 0 && y < W && a[x][y] != '.');
}
void solve(){
cin >> H >> W;
a = vector<vector<char>>(H, vector<char>(W));
rep(i, 0, H){
string s; cin >> s;
rep(j, 0, W){
a[i][j] = s[j];
}
}
deque<pii> q;
q.push_front({0, 0});
vector<vector<int>> d(H, vector<int>(W, INT_MAX));
d[0][0] = 1;
int ans = 1;
while(!q.empty()){
auto [x, y] = q.front();
q.pop_front();
rep(i, 0, 4){
int x2 = x + dx[i], y2 = y + dy[i];
if(valid(x2, y2)){
if(a[x2][y2] != a[x][y] && d[x2][y2] > d[x][y] + 1){
d[x2][y2] = d[x][y] + 1;
q.push_back({x2, y2});
} else if(a[x2][y2] == a[x][y] && d[x2][y2] > d[x][y]){
d[x2][y2] = d[x][y];
q.push_front({x2, y2});
}
}
}
ans = max(ans, d[x][y]);
}
cout << ans;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
solve();
return 0;
}
