#include <iostream>
#include <fstream>
using namespace std;
int n,m,i,j,elem_max,dp[1<<9],sol;
char v[1<<9][1<<9];
int main()
{
    cin>>n>>m;
    for(i=1;i<=n;++i) cin>>(v[i]+1);
    for(i=1;i<=n;++i)
    {
        int secv=0;
        for(j=1;j<=m;++j)
        {
            if(v[i][j]=='1') secv++;
            else
            {
                secv=0;
                elem_max=0;
            }
            if(secv>1)
            {
                for(int k=j-secv+1;k<j;++k)
                    sol=max(sol,j-k+dp[k]+dp[j]);
            }
            if(v[i][j]=='1') dp[j]++;
            else dp[j]=0;
        }
    }
    cout<<sol;
    return 0;
}