#include<bits/stdc++.h>
using namespace std;
namespace BSS
{
	#define ll long long int
	#define re register ll 
	#define lf double
	#define lb lower_bound 
	#define ub upper_bound 
	#define mp make_pair
	#define File(x,y) freopen(#x,"r",stdin),freopen(#y,"w",stdout)
	#define Fill(x,y) memset(x,y,sizeof x);
	#define Copy(x,y) memcpy(x,y,sizeof x);
	inline ll read()
	{
		ll ss=0; bool cit=1; char ch;
		while(!isdigit(ch=getchar())) if(ch=='-') cit=0;
		while(isdigit(ch)) ss=(ss<<3)+(ss<<1)+(ch^48),ch=getchar();
		return cit?ss:-ss;
	}
} using namespace BSS;

const ll N=2051;
ll m,n,s,ans;
ll pre[N][N];
char ch[N];
signed main(){
	n=read(); s=read();
	for(re i=1;i<=n;i++){
		scanf("%s",ch+1);
		for(re j=1;j<=n;j++)
			pre[i][j]=pre[i-1][j]+pre[i][j-1]-pre[i-1][j-1]+ch[j]-'0';
	}
	ll temp;
	for(re i=s;i<=n;i++){
		for(re j=s;j<=n;j++){
			temp=pre[i][j]-pre[i-s][j]-pre[i][j-s]+pre[i-s][j-s];
			ans=max(ans,temp);
		}
	}
	printf("%lld",ans);
	return 0;
}