#include <bits/stdc++.h>
using namespace std;
#define ll long long
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int H, W, dx[4]{0, 1, 0, -1}, dy[4]{1, 0, -1, 0};
cin >> H >> W;
char grid[H][W];
for(int i=0; i<H; ++i) {
for(int j=0; j<W; ++j) {
cin >> grid[i][j];
}
}
deque<pair<int, int>> dq;
int dist[H][W], ans=0;
memset(dist, 0, sizeof(dist));
dist[0][0]=1;
dq.push_front({0, 0});
while(!dq.empty()) {
pair<int, int> p=dq.front();
dq.pop_front();
int r=p.first, c=p.second;
ans=max(ans, dist[r][c]);
for(int i=0; i<4; ++i) {
int u=r+dx[i], v=c+dy[i];
if(u<0||u>=H||v<0||v>=W||dist[u][v]||grid[u][v]=='.')
continue;
if(grid[u][v]!=grid[r][c]) {
dist[u][v]=dist[r][c]+1;
dq.push_back({u, v});
}
else {
dist[u][v]=dist[r][c];
dq.push_front({u, v});
}
}
}
cout << ans;
}
