#include<bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
#define endl "\n"
#define mod 1000000007
using ll = long long;
using namespace std;
const string NoF = "Name_of_File";
int h, w;
vector<vector<int>> grid(4000,vector<int>(4000,0));
int dx[4] = {0,0,1,-1};
int dy[4] = {1,-1,0,0};
bool inside(int x, int y) {
return (0 <= x && x < h && 0 <= y && y < w && grid[x][y] == 0);
}
void solve() {
cin >> h >> w;
vector<string> snow(h);
for (string &x : snow) cin >> x;
deque<pair<int,int>> dq;
dq.push_back({0,0});
grid[0][0] = 1;
int kq = 0;
while (!dq.empty()) {
auto [u,v] = dq.front();
dq.pop_front();
kq = max(kq,grid[u][v]);
for (int i = 0 ; i < 4; i++) {
int x = u + dx[i], y = v + dy[i];
if (!inside(x,y) || snow[x][y] == '.' ) continue;
if (snow[u][v] == snow[x][y]) {
dq.push_front({x,y});
grid[x][y] = grid[u][v];
}
else {
dq.push_back({x,y});
grid[x][y] = grid[u][v] + 1;
}
}
}
cout << kq;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
// freopen((NoF + ".in").c_str(),"r",stdin);
// freopen((NoF + ".out").c_str(),"w",stdout);
solve();
}
