#include <bits/stdc++.h>
using namespace std;
int di[4] = {1, -1, 0, 0};
int dj[4] = {0, 0, 1, -1};
int main() {
cin.tie(0)->sync_with_stdio(0);
int H, W;
cin >> H >> W;
vector<string> grid(H);
for (int i=0; i<H; i++) cin >> grid[i];
vector<vector<int>> dist(H, vector<int>(W, -1));
deque<pair<int,int>> Q;
dist[H-1][W-1] = 1;
Q.push_back({H-1, W-1});
while (Q.size()) {
auto [i, j] = Q.front(); Q.pop_front();
for (int k=0; k<4; k++) {
int i2 = i + di[k];
int j2 = j + dj[k];
if (i2 < 0 || j2 < 0 || i2 >= H || j2 >= W) continue;
if (grid[i2][j2] == '.') continue;
int d = dist[i][j] + (grid[i][j] != grid[i2][j2]);
if (dist[i2][j2] == -1 || d < dist[i2][j2]) {
dist[i2][j2] = d;
if (grid[i][j] == grid[i2][j2]) Q.push_front({i2, j2});
else Q.push_back({i2, j2});
}
}
}
int ans = 0;
for (int i=0; i<H; i++) {
for (int j=0; j<W; j++) {
ans = max(ans, dist[i][j]);
}
}
cout << ans << "\n";
return 0;
}
