#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    int x;
    int y;
} Point;

int main() {
    int N, M;
    scanf("%d %d", &N, &M);

    int** paper = (int**)malloc(sizeof(int*)*N);
    int cheese = 0;
    int time = 0;

    for(int i=0; i<N; i++) {
        paper[i] = (int*)malloc(sizeof(int)*M);

        for(int j=0; j<M; j++) {
            scanf("%d",&paper[i][j]);

            if(paper[i][j] == 1) cheese++;
        }
    }

    int** visited = (int**)malloc(sizeof(int*)*N);
    for(int i=0; i<N; i++) visited[i] = (int*)malloc(sizeof(int)*M);
    Point* qu = (Point*)malloc(sizeof(Point)*(N*M));

    while(cheese != 0) {
        for(int i=0; i<N; i++) memset(visited[i], 0, sizeof(int)*M);

        int q_front = 0;
        int q_rear = 0;

        Point start = {0,0};
        qu[q_rear++] = start;
        visited[0][0] = 1;

        int dx[4] = {-1,1,0,0};
        int dy[4] = {0,0,1,-1};

        while(q_front != q_rear) {
            Point now = qu[q_front++];

            for(int i=0; i<4; i++) {
                int nx = now.x + dx[i];
                int ny = now.y + dy[i];

                if(0<=nx && nx<M && 0<=ny && ny<N && paper[ny][nx] == 0 && visited[ny][nx] == 0) {
                    Point next = {nx, ny};
                    qu[q_rear++] = next;
                    visited[ny][nx] = 1;

                    for(int j=0; j<4; j++) {
                        int nnx = next.x + dx[j];
                        int nny = next.y + dy[j];

                        if(0<=nnx && nnx<M && 0<=nny && nny<N && paper[nny][nnx] == 1) visited[nny][nnx]++; 
                    }
                }
            }
        }

        for(int i=0; i<N; i++) {
            for(int j=0; j<M; j++) {
                if(paper[i][j] == 1 && visited[i][j] > 1) {
                    paper[i][j] = 0;
                    cheese--;
                }
            }
        }

        time++;
    }

    printf("%d\n",time);

    for(int i=0; i<N; i++) free(paper[i]);
    free(paper);
    for(int i=0; i<N; i++) free(visited[i]);
    free(visited);
    free(qu);

    return 0;
}