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

long M,N;
char a[100][100];
int b[100][100];
int size[10000],nr;

void ReadData(void){
  FILE *f = fopen("GAURI.IN","rt");
  fscanf(f,"%ld%ld",&M,&N);
  for (int i=0;i<M;i++)
    fscanf(f,"%s",a[i]);
  fclose(f);
}

void FillHole(int i,int j, int nr){
  b[i][j] = nr;
  size[nr]++;
  int dx[]={-1,0,1,0};
  int dy[]={0,-1,0,1};
  for (int k=0;k<4;k++){
    int ii = i+dx[k];
    int jj = j+dy[k];
    if (ii>=0 && jj>=0 && ii<M && jj<N)
      if (a[ii][jj]=='0')
	if (!b[ii][jj])
	  FillHole(ii,jj,nr);
  }
}

void FindSolution(void){
  for (int i=0;i<M;i++)
    for (int j=1;j<N;j++)
      if (a[i][j]=='0' && !b[i][j]){
	FillHole(i,j,nr+1);
	nr++;
      }
  for (i=0;i<M;i++){
    size[b[i][0]]=0;
    size[b[i][N-1]]=0;
  }
  for (i=0;i<N;i++){
    size[b[0][i]]=0;
    size[b[M-1][i]]=0;
  }
}

void WriteSolution(void){
  FILE *f=fopen("GAURI.OUT","wt");
  int max=size[1];
  for (int i=2;i<nr;i++)
    if (max<size[i])
      max = size[i];
  fprintf(f,"%d",max);
  fclose(f);
}

void main(void){
  ReadData();
  FindSolution();
  WriteSolution();
}