#include <bits/stdc++.h>
using namespace std;
const int mxN = 4002;
char mat[mxN][mxN];
int dist[mxN][mxN];
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
const int INF = 1e9 + 12;
int main() {
int h, w;
cin >> h >> w;
for (int i = 0; i < h; ++i) {
for (int j = 0; j < w; ++j) {
cin >> mat[i][j];
dist[i][j] = INF;
}
}
deque<pair<int, int>> q;
q.push_front({h-1, w-1});
dist[h-1][w-1] = 1;
auto check = [&](int x, int y) {
return x >= 0 && x < h && y >= 0 && y < w;
};
while(!q.empty()) {
auto tren = q.front();
q.pop_front();
for(int i = 0; i < 4; ++i) {
if(!check(tren.first+dx[i], tren.second+dy[i])) continue;
int nx = tren.first+dx[i];
int ny = tren.second+dy[i];
if(mat[nx][ny] == '.') continue;
if(dist[nx][ny] != INF) continue;
if(mat[nx][ny] != mat[tren.first][tren.second]) {
dist[nx][ny] = dist[tren.first][tren.second] + 1;
q.push_back({nx, ny});
} else {
dist[nx][ny] = dist[tren.first][tren.second];
q.push_front({nx, ny});
}
}
}
int ans = 0;
for(int i = 0; i < h; ++i) {
for(int j = 0; j < w; ++j) {
if(dist[i][j] == INF) continue;
ans = max(ans, dist[i][j]);
}
}
cout << ans << '\n';
}
