#include <bits/stdc++.h>

using namespace std;

int up[512][512];
char x[512][512];

int main() {
    int n, m;
    scanf("%d %d\n", &n, &m);
    for (int i = 1; i <= n; ++i)
        gets(x[i] + 1);
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
            if (x[i][j] == '0')
                up[i][j] = 0;
            else
                up[i][j] = 1 + up[i - 1][j];
    int res = 0;
    for (int i = 1; i <= n; ++i) {
        int pizda = 0;
        for (int j = m; j >= 1; --j)
            if (x[i][j] == '0')
                pizda = 0;
            else {
                if (pizda == 0) {
                    if (up[i][j] != 1)
                        pizda = up[i][j];
                } else {
                    if (pizda + up[i][j] > res && up[i][j] != 1)
                        res = pizda + up[i][j];
                    if (up[i][j] > pizda)
                        pizda = up[i][j];
                    ++pizda;
                }
            }
    }
    if (res < 4)
        res = 0;
    printf("%d", res);
    return 0;
}