#include <vector>
#include <iostream>
using namespace std;

class Solution {
public:
    int maxAreaOfIsland(vector<vector<int> >& grid);
};

int DFS(int i, int j, vector < vector <int> > &g)
{
  int c;

  if (g[i][j] == 1) {
    g[i][j] = 0;
    c = 1;
    if (i != 0) c += DFS(i-1, j, g);
    if (i+1 != g.size()) c += DFS(i+1, j, g);
    if (j != 0) c += DFS(i, j-1, g);
    if (j+1 != g[0].size()) c += DFS(i, j+1, g);
    return c;
  }
  return 0;
}

int Solution::maxAreaOfIsland(vector<vector<int> >& g)
{
  int i, j, cs;
  int max = 0;

  for (i = 0; i < g.size(); i++) {
    for (j = 0; j < g[0].size(); j++) {
      if (g[i][j] == 1) {
        cs = DFS(i, j, g);
        if (cs > max) max = cs;
      }
    }
  }
  return max;
}

/* To use the main, enter row cols and then the grid. */

int main()
{
  int r, c, n;
  int i, j;
  vector < vector < int > > g;
  Solution s;

  cin >> r >> c;

  g.resize(r);
  for (i = 0; i < r; i++) {
    for (j = 0; j < c; j++) {
      cin >> n;
      g[i].push_back(n);
    }
  }

  n = s.maxAreaOfIsland(g);
  cout << n << endl;
}