#include <iostream>
#include <vector>

using namespace std;

typedef vector<vector<int>> matrica;

int obala(matrica &mat, int n, int m, int i, int j) {
    if(i < 0 || j < 0 || i >= n || j >= m || mat[i][j] == 0) {
        return 1;
    }
    if(mat[i][j] == 2) return 0;

    mat[i][j] = 2;

    int o = obala(mat, n, m, i+1, j);
       o += obala(mat, n, m, i,   j-1);
       o += obala(mat, n, m, i-1, j);
       o += obala(mat, n, m, i,   j+1);
    return o;
}

int main() {
    int n, m;
    cin >> n >> m;

    matrica mat(n, vector<int>(m));
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < m; j++) {
            cin >> mat[i][j];
        }
    }

    int max_obala = 0;
    int jedna_obala;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < m; j++) {
            if(mat[i][j] == 1) {
                jedna_obala = obala(mat, n, m, i, j);
                if(jedna_obala > max_obala) max_obala = jedna_obala;
            }
        }
    }

    cout << max_obala << endl;
}