#include <bits/stdc++.h>
using namespace std;
const int MAXN = 4001;
const int dx[] = {-1, 1, 0, 0};
const int dy[] = {0, 0, -1, 1};
char mat[MAXN][MAXN];
int dist[MAXN][MAXN], n, m;
bool inside(int x, int y) {
return (x >= 1 && x <= n && y >= 1 && y <= m && mat[x][y] != '.');
}
int main() {
cin >> n >> m;
for(int i = 1; i <= n; i++)
for(int j = 1; j <= m; j++)
cin >> mat[i][j];
deque<pair<int,int>> dq;
dq.emplace_back(1, 1);
dist[1][1] = 1;
int answer = 1;
while(!dq.empty()) {
int l = dq.front().first;
int c = dq.front().second;
dq.pop_front();
answer = max(answer, dist[l][c]);
for(int k = 0; k < 4; k++) {
int nxtl = l + dx[k];
int nxtc = c + dy[k];
if(inside(nxtl, nxtc) && !dist[nxtl][nxtc]) {
if(mat[l][c] != mat[nxtl][nxtc]) { // weight 1
dist[nxtl][nxtc] = dist[l][c] + 1;
dq.emplace_back(nxtl, nxtc);
} else {
dist[nxtl][nxtc] = dist[l][c];
dq.push_front({nxtl, nxtc});
}
}
}
}
cout << answer << '\n';
return 0;
}
