#define _CRT_SECURE_NO_DEPRECATE
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>

/*

*/

using namespace std ;

typedef long long LL ;
typedef unsigned long long ULL ;
typedef unsigned int uint;
typedef unsigned char uchar;

typedef vector<int>     vi  ;
typedef vector<vi>     vvi  ;
typedef vector<string>  vs  ;
typedef vector<vs>     vvs  ;

typedef pair<string,string> pss ;
typedef pair<double, double> pdd;
typedef pair<int,int>  pii  ;
typedef pair<LL,LL> pll ;
typedef pair<ULL, ULL> puu;

#define all(V) (V).begin(), (V).end()
#define allr(V) (V).rbegin(), (V).rend()
#define SET(Adr,val) memset(Adr,val,sizeof(Adr))
#define SET0(Adr) memset(Adr,0,sizeof(Adr))
#define CMP(Adr1,Adr2) memcmp(&Adr1,&Adr2,sizeof(Adr1))

#define FOR(it,a,b)  for( int(it) = (int)a ; it<= (int(b)) ; ++it )
#define FORN(it,a,b) for( int(it) = (int)a ; it<  (int(b)) ; ++it )
#define FORV(it,v)   for( it = (v).begin() ; it!=(v).end() ; ++it )

#define FORMI(i,j,ii,jj,im,jm) for( int(i) = (int)ii ; i < (int)im ; ++i )\
                               for( int(j) = (int)jj ; j < (int)jm ; ++j )

#define FORMO(i,j,ii,jj,im,jm) for( int(i) = (int)ii ; i < (int)im ; ++i, cout << '\n')\
                               for( int(j) = (int)jj ; j < (int)jm ; ++j, cout << ' ' )

#define SHOWME(x) cerr << __LINE__ << ": " << #x << " = " << (x) <<'\n';
#define inchide cerr << "\nLine "<< __LINE__ << " just passed...EXIT\n" ;exit(-1);
#define Cat(a,b) ((double(a))/(double(b)))
#define Min(a,b) (((a)>(b))?(b):(a))
#define Max(a,b) (((a)>(b))?(a):(b))
#define Prod(a,b) (((a)*(b)))
#define Pow2(a) (((a)*(a)))
#define sz(x) ((int)(x).size())
#define forn(i,n) for(int i=0;i<(n);++i)
#define fors(i,v) forn(i,sz(v))
#define MOD1 1000000007
#define NMAX 10000
#define NMAX2 20001
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define left asdleft
#define right asdright
#define link asdlink
#define unlink asdunlink
#define next asdnext
#define prev asdprev

const double Euler =  2.71828182845904523536 ;
const double PI    =  3.14159265358979323846 ;
const double EPS = 1e-10;
const int INF = 0x3fefefef ;
const double DINF = 1e200;
const LL LINF = INF*1ll*INF;

const int dx[4] = { 0 ,-1 , 0 ,1 } ;
const int dy[4] = { 1 , 0 ,-1 ,0 } ;

                    /* |V1|  |E3|   |SV5|   |SE7| */
const int dx8[8] = { 0 ,-1 ,0  ,1 ,1 ,-1 ,-1 , 1 } ;
const int dy8[8] = { 1 , 0 ,-1 ,0 ,1 ,-1 , 1 ,-1 } ;
                /* |N0|   |S2|  |NE4|   |NV6| */

template<class T> inline ostream& operator<<(ostream &out,const pair<T,T>&__p)
{return(out<<__p.fi<<' '<<__p.se<<'\n');}
template<class T> inline istream& operator>>(istream &in,pair<T,T>&__p)
{in>>__p.fi>>__p.se;return(in);}
template<class T,class F> inline ostream& operator<<(ostream &out ,const pair<T,F>&__p){
(out<<__p.fi<<' '<<__p.se<< '\n');}
template<class T,class F> inline istream& operator>>(istream &in ,pair<T,F>&__p){
in>>__p.fi>>__p.se;return(in);}
inline int toint(const string &s){istringstream iss(s);int res;iss>>res;return(res);}
inline double dist2pct(int _x,int _y,int _z,int _w){return(sqrt(Pow2(_z-_x)+Pow2(_w-_y)));}
template<class T>inline string tostr(const T &x){ostringstream ss;ss<<x;return(ss.str());}
template<class T>inline ostream& arata(ostream &out ,const T &a){return(out<<a<<'\n');}
template<class T>inline istream& citeste(istream &in ,T &a){return(in>>a);}
template<class T>void AddNr(T &a, T b){a=a+b;while(a>=MOD1)a-=MOD1;while(a<0)a+=MOD1;}
template<class T>void ReadNo(T&__no){T __sign=1;char ch;__no=0;
while(!isdigit(ch=getchar()))(ch=='-')&&(__sign=-1);
do{__no=(__no<<1)+(__no<<3)+(ch-48);}while(isdigit(ch=getchar()));__no*=__sign;}
template<class T>struct Functor{T __A,__B ;
inline bool operator() (T __A , T __B ){return  (__A >__B) ;}};


/******************************************************************************************/

#define DIM  512
int n , m ;
int M[DIM][DIM] ;
int A[DIM][DIM]  , UP[DIM][DIM] , LU[DIM][DIM] ;
void Citire()
{
//    FILE * f = fopen("file.in" , "r");

    fscanf(stdin,"%d%d",&n,&m);
    fgetc(stdin);

    char line[256] ;

    FOR( i, 1, n )
    {
        fgets(line+1,sizeof(line) ,stdin);
        FOR( j, 1, m )
            A[i][j] = (line[j]- '0');
    }

//    fclose(f);
}

/******************************************************************************************/

/** MAIN **/
int main(){
    Citire();

    FOR ( i , 1 , n )
        FOR ( j , 1 , m )
            if (A[i][j])
            {
                UP[i][j] = UP[i-1][j] + 1 ;
                if (!A[i - 1][j]) UP[i][j] = 0;
                else if (!UP[i - 1][j]) ++UP[i][j];

                if (LU[i][j - 1]) LU[i][j] = LU[i][j - 1] + 1;
                if (UP[i][j - 1]) LU[i][j] = max (LU[i][j], UP[i][j - 1] + 1);

            }


    int a = 0 , s = -1 ;
    FOR ( i , 1 , n )
        FOR ( j , 1 , m )
            if ( LU[i][j] && UP[i][j] )
            {
                a = LU[i][j] + UP[i][j] - 1 ;
                if ( a > s )s = a ;

            }

    printf("%d\n" ,((s<4) ? 0 : s ) );


    return(0);
}
/** MAIN **/