#include <bits/stdc++.h>

using namespace std;

const int NMax = 505;

int v[NMax][NMax];

int main(){
    #ifndef ONLINE_JUDGE
    freopen("debug.in", "r", stdin);
    #endif // ONLINE_JUDGE

    int n, m;
    string S;
    cin >> n >> m;
    for(int i = 1; i <= n; i++){
        cin >> S;
        for(int j = 1; j <= m; j++){
            v[i][j] = S[j - 1] - '0';
        }
    }
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            if(v[i][j]){
                v[i][j] += v[i - 1][j];
            }
        }
    }
    int best = 0;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            if(v[i][j] > 1){
                for(int k = j + 1; k <= m && v[i][k]; k++){
                    if(v[i][k] > 1){
                        best = max(best, v[i][j] + v[i][k] + (k - j - 1));
                    }
                }
            }
        }
    }
    cout << best;
    return 0;
}