#include<bits/stdc++.h>

using namespace std;

int maxi, N, M, up[509][509];
char sir[509][509];

int pow (int a, int b, int mod)
{
    int p = 1;
    for (int i=0; (1<<i) <= b; i++)
    {
        if (b & (1 << i)) p = (1LL * p * a) % mod;
        a = (1LL * a * a) % mod;
    }
    return p;
}

void Try (int i, int st, int dr)
{
    int bst = up[i][st] - st;
    for (int j=st + 1; j<=dr; j++)
    {
        if (up[i][j] + j + bst - 1 > maxi)
            maxi = up[i][j] + j + bst - 1;
        if (up[i][j] - j > bst) bst = up[i][j] - j;
    }
}

int main()
{
//freopen ("input", "r", stdin);
//freopen ("output", "w", stdout);

scanf ("%d %d\n", &N, &M);
for (int i=1; i<=N; i++)
    gets (sir[i] + 1);
for (int i=1; i<=N; i++)
{
    for (int j=1; j<=M; j++)
        if (sir[i][j] == '0') up[i][j] = 0;
        else up[i][j] = up[i - 1][j] + 1;
    for (int j=1; j<=M; j++)
        if (sir[i][j] == '1')
        {
            int k=j;
            for (k=j; k<=M; k++)
                if (sir[i][k] == '0') break;
            k --;
            Try (i, j, k), j = k;
        }
}
printf ("%d\n", maxi);

return 0;
}