#define _CRT_SECURE_NO_DEPRECATE
#include <queue>
#include <cstdio>

using namespace std;
typedef pair<int, int> pii;

int n, m;
bool used[31][31] = {0};
int dx[] = {0, 0, 1, -1};
int dy[] = {-1, 1, 0, 0};

int bfs(pii from) {
    int res = 1;
    queue <pii> q;
    used[from.first][from.second] = true;
    q.push(from);
    while (!q.empty()) {
        pii cur = q.front();
        q.pop();
        for (int i = 0; i < 4; i++) {
            pii to = cur;
            to.first += dx[i];
            to.second += dy[i];
            if (to.first > n - 1 || to.first < 0) continue;
            if (to.second > m - 1 || to.second < 0) continue;
            if (used[to.first][to.second]) continue;
            q.push(to);
            res++;
            used[to.first][to.second] = true;
        }
    }
    return res;
}

int main() {
    freopen("test.in", "r", stdin);
    freopen("test.out", "w", stdout);
    int maxval = 0;
    scanf("%d %d ", &n, &m);
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++) {
            char x;
            scanf("%c ", &x);
            if (!(x - '0')) continue;
            used[i][j] = true;
        }
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++) {
            if (used[i][j]) continue;
            int cur = bfs(pii(i, j));
            maxval = cur > maxval ? cur : maxval;
        }
    printf("%d", maxval);
    return 0;
}