#include <iostream>

using namespace std;

const int NMAX = 510;

char a[NMAX][NMAX];
int v[NMAX][NMAX], h[NMAX][NMAX];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n, m;
    cin >> n >> m;
    cin.get();
    for (int i = 1; i <= n; ++i) {
        cin.getline(a[i] + 1, 502);
    }
    for (int i = 1; i <= n; ++i) {
        for (int j = m; j; --j) {
            if (a[i][j] == '0') {
                v[i][j] = 0;
                h[i][j] = 0;
            }
            else {
                v[i][j] = v[i - 1][j] + 1;
                h[i][j] = h[i][j + 1] + 1;
            }
        }
    }
    int lmax = 0;
    for (int i = 2; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (v[i][j] && h[i][j]) {
                for (int k = j + 1; k < j + h[i][j]; ++k) {
                    lmax = max(lmax, v[i][j] + k - j - 1 + v[i][k]);
                }
            }
        }
    }
    cout << lmax << '\n';
    return 0;
}