#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <cstring>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <queue>
using namespace std;

const int N = 1000;
char s[N][N];
int up[N][N];

int main() {
    int n, m;
    cin >> n >> m;
    for(int i = 0; i < n; ++i)
        scanf("%s", s[i]);
    for(int j = 0; j < m; ++j) {
        for(int i = 0; i < n; ++i) {
            up[i][j] = (i > 0 ? up[i-1][j] : -1) + 1;
            if(s[i][j] == '0') up[i][j] = -1;
        }
    }
    int ans = 0;
    for(int i = 0; i < n; ++i) {
        for(int j1 = 0; j1 < m; ++j1) {
            if(s[i][j1] == '0' || up[i][j1] <= 0) continue;
            for(int j2 = j1 + 1; j2 < m; ++j2) {
                if(s[i][j2] == '0') break;
                if(up[i][j2] <= 0) continue;
                ans = max(ans, up[i][j1] + up[i][j2] + j2 - j1 + 1);
            }
        }
    }
    cout << ans << endl;
    
    
    
    return 0;
}

/*


*/