#include <bits/stdc++.h>
using namespace std;
int n,m,i,j,cur,r,a[505];
char s[505];
int main() {
  scanf("%d%d",&n,&m);
  for (i=1; i<=n; i++) {
    scanf("%s",s);
    for (cur=j=0; j<m; j++) if (s[j]=='1') {
      a[j]++;
      if (cur) {
        if (a[j]>1) {
          r=max(r,cur+a[j]);
          cur=max(cur,a[j]-1);
        }
        cur++;
      } else if (a[j]>1) cur=a[j];
    } else a[j]=cur=0;
  }
  printf("%d\n",r);
  return 0;
}