251215_2638_치즈_G3_DFS

//O((NM)^2)
//dfs이용 별거 없음. 바깥에 있는 치즈를 찾기 위해 바깥쪽만 쭉 돌면서 dfs로 바깥 치즈를 찾음.
#include <iostream>
#include <vector>

using namespace std;

int N, M;
int result = 0;

vector<vector<int>> arr;
vector<vector<int>> visited;
int dirx[] = { 0,0,-1,1 };
int diry[] = { 1,-1,0,0 };

void dfs(int x,int y) {
	visited[x][y] = -1;
	for (int i = 0; i < 4; i++) {
		int forx = dirx[i] + x;
		int fory = diry[i] + y;
		if (forx < 0 or forx >= N or fory < 0 or fory >= M) continue;
		
		if (visited[forx][fory] == 0 and arr[forx][fory] == 0) dfs(forx, fory);
		if (arr[forx][fory] == 1) visited[forx][fory]++;
	}
}

void melt_cheese() {
	visited.assign(N, vector<int>(M, 0));
	for (int i = 0; i < N; i++) {
		if (visited[i][0] == 0)
			dfs(i, 0);
		if (visited[i][M - 1] == 0)
			dfs(i, N - 1);
	}
	for (int i = 0; i < M; i++) {
		if (visited[0][i] == 0)
			dfs(i, 0);
		if (visited[N-1][i] == 0)
			dfs(i, N - 1);
	}



	int cnt = 0;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < M; j++) {
			if (visited[i][j] >= 2) {
				arr[i][j] = 0;
				cnt++;
			}
		}
	}
	if (cnt > 0) {
		result++;
		melt_cheese();
	}

}



int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	cin >> N >> M;
	arr.assign(N, vector<int>(M, 0));
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < M; j++) {
			cin >> arr[i][j];
		}
	}
	melt_cheese();
	cout << result;
	

}