#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
const int inf = 1e9;
const int rc[]{0,0,1,-1};
const int cc[]{1,-1,0,0};
const int N = 4004;
char a[N][N];
int n,m, d[N][N];
void solve() {
cin >> n >> m;
int ok = 0, ok1 = 0;
for (int i = 0; i < n;i++) {
for (int j = 0; j < m;j++) {
cin >> a[i][j];
}
}
memset(d,-1,sizeof(d));
deque<ar<int,2>> q;
q.push_back({0,0});
int ans = 0;
d[0][0] = 1;
while (!q.empty()) {
auto [x,y] = q.front();
q.pop_front();
ans = max(ans,d[x][y]);
for (int i = 0; i < 4;i++) {
int nx = rc[i] + x, ny = cc[i] + y;
if (nx >= 0 && ny >= 0 && nx < n && ny < m && a[nx][ny] != '.') {
if (d[nx][ny] == -1) {
if (a[nx][ny] == a[x][y]) {
d[nx][ny] = d[x][y];
q.push_front({nx,ny});
}else {
d[nx][ny] = d[x][y] + 1;
q.push_back({nx,ny});
}
}
}
}
}
cout << ans;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
cout << "\n";
}
return 0;
}
