#include <bits/stdc++.h>
#define f first
#define s second
using namespace std;
void fastIO() {ios_base::sync_with_stdio(false), cin.tie(nullptr);}
const int INF = 1e9;
const int MAXR = 4001;
const int MAXC = 4001;
const int dr[4] = {0, 1, 0, -1}, dc[4] = {1, 0, -1, 0};
int R, C;
char grid[MAXR][MAXC];
int dist[MAXR][MAXC];
int ans = 0;
signed main() {
fastIO();
cin >> R >> C;
char on;
for (int r = 0; r < R; r++) {
for (int c = 0; c < C; c++) {
cin >> on;
grid[r][c] = on;
}
}
if (grid[0][0] == '.') {
cout << "0\n";
return 0;
}
for (int r = 0; r < R; r++) {
for (int c = 0; c < C; c++) {
dist[r][c] = INF;
}
}
dist[0][0] = 1;
deque<pair<int, int>> DQ;
DQ.push_back({0, 0});
pair<int, int> p;
int r, c;
while (!DQ.empty()) {
p = DQ.front();
r = p.f, c = p.s;
DQ.pop_front();
for (int i = 0; i < 4; i++) {
if (0 > r + dr[i] || r + dr[i] >= R || 0 > c + dc[i] || c + dc[i] >= C) continue;
if (grid[r + dr[i]][c + dc[i]] == '.') continue;
if (grid[r + dr[i]][c + dc[i]] == grid[r][c] && dist[r + dr[i]][c + dc[i]] > dist[r][c]) {
dist[r + dr[i]][c + dc[i]] = dist[r][c];
DQ.push_front({r + dr[i], c + dc[i]});
}
else if (dist[r + dr[i]][c + dc[i]] > dist[r][c] + 1) {
dist[r + dr[i]][c + dc[i]] = dist[r][c] + 1;
DQ.push_back({r + dr[i], c + dc[i]});
}
ans = max(ans, dist[r + dr[i]][c + dc[i]]);
}
}
cout << ans << "\n";
}
