#include <bits/stdc++.h>
using namespace std;
#define fast ios::sync_with_stdio(0);cin.tie(0);
typedef long long ll;
#define f first
#define s second
#define MOD 1000000007
#define LOGN 20
#define MAXN 1000005
const int delRow[] = {-1, 0, 0, 1};
const int delCol[] = {0, -1, 1, 0};
int H, W;
vector<string> grid;
int main() {
fast
cin >> H >> W;
grid = vector<string>(H);
for (int i = 0; i < H; i++)
cin >> grid[i];
vector<vector<int>> depth(H, vector<int>(W, 0));
deque<pair<int,int>> dq;
dq.push_back({0, 0});
depth[0][0] = 1;
int ans = 0;
while (dq.size()) {
int row = dq.front().f;
int col = dq.front().s;
ans = max(ans, depth[row][col]);
dq.pop_front();
for (int i = 0; i < 4; i++) {
int nRow = row + delRow[i];
int nCol = col + delCol[i];
if (nRow >= 0 && nRow < H && nCol >= 0 && nCol < W && grid[nRow][nCol] != '.' && depth[nRow][nCol] == 0) {
if (grid[row][col] == grid[nRow][nCol]) {
depth[nRow][nCol] = depth[row][col];
dq.push_front({nRow, nCol});
} else {
depth[nRow][nCol] = depth[row][col] + 1;
dq.push_back({nRow, nCol});
}
}
}
}
cout << ans << "\n";
}
