foto

#include <iostream>
using namespace std;

int Width, Height, lim;
bool mat[100][100];
int maxi = -1;

void Process(int Y, int X) {
    mat[Y][X] = 1;
    if (X + 1 <= Width - 1)
    if (mat[Y][X + 1] == 0) {
        lim++;
        Process(Y, X + 1);
    }

    if (X - 1 >= 0)
    if (mat[Y][X - 1] == 0) {
        lim++;
        Process(Y, X - 1);
    }

    if (Y - 1 >= 0)
    if (mat[Y - 1][X] == 0) {
        lim++;
        Process(Y - 1, X);
    }

    if (Y + 1 <= Height - 1)
    if (mat[Y + 1][X] == 0) {
        lim++;
        Process(Y + 1, X);
    }
}

int main() {
    cin >> Width >> Height;
    for (int i = 0; i <= Height - 1; i++)
        for (int k = 0; k <= Width - 1; k++)
            cin >> mat[i][k];

    for (int i = 0; i <= Height - 1; i++)
        for (int k = 0; k <= Width - 1; k++) {
            if (mat[i][k] == 0) {
                lim = 1;
                Process(i, k);
                if (lim > maxi)
                    maxi = lim;
            }
        }

    cout << maxi;
}