static int[] yy = {-1, 0, 1, 0}, xx = {0, 1, 0, -1};

static int N, M, K;

static int[][] A, G;

static ArrayList<Integer>[] con;

static void color(int y, int x) {

for (int dir=0;dir<4;dir++){

int ny = y + yy[dir], nx = x + xx[dir];

if (ny < 1 || ny > N || nx < 1 || nx > M || A[ny][nx] != A[y][x] || G[ny][nx] != 0) continue;

G[ny][nx] = G[y][x];

color(ny, nx);

}

}

static int bfs(int st) {

int[] D = new int[K+1];

for (int i=1;i<=K;i++) D[i] = Integer.MAX_VALUE;

Queue <Integer> que = new LinkedList<Integer>();

que.add(st); D[st] = 0;

while (!que.isEmpty()){

int q = que.poll();

for (int t: con[q]){

if (D[t] < Integer.MAX_VALUE) continue;

D[t] = D[q]+1; que.add(t);

}

}

int ret = 0;

for (int i=1;i<=K;i++) ret = Math.max(ret, D[i]);

return ret;

}

public static void main(String[] args) throws Exception {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

StringTokenizer st = new StringTokenizer(br.readLine());

N = Integer.parseInt(st.nextToken());

M = Integer.parseInt(st.nextToken());

A = new int[N+1][M+1];

for (int i=1;i<=N;i++){

st = new StringTokenizer(br.readLine());

for (int j=1;j<=M;j++) A[i][j] = Integer.parseInt(st.nextToken());

}

G = new int[N+1][M+1];

for (int i=1;i<=N;i++) for (int j=1;j<=M;j++) if (G[i][j] == 0){

G[i][j] = ++K;

color(i, j);

}

con = new ArrayList[K+1];

for (int i=1;i<=K;i++) con[i] = new ArrayList<Integer>();

for (int i=1;i<=N;i++) for (int j=1;j<=M;j++){

for (int dir=0;dir<4;dir++){

int y = i + yy[dir], x = j + xx[dir];

if (y < 1 || y > N || x < 1 || x > M || A[y][x] == A[i][j]) continue;

con[G[i][j]].add(G[y][x]);

}

}

int ans = Integer.MAX_VALUE;

for (int i=1;i<=K;i++) ans = Math.min(ans, bfs(i));

System.out.println(ans);

}