#include <bits/stdc++.h>
using namespace std;

using ll=long long;
const ll inf=0x3f3f3f3f3f3f3f3f;
const int N=705;
ll a[N][N];
int main()
{
	ios::sync_with_stdio(0);cin.tie(0);
	int n,K;cin>>n>>K;
    memset(a,0,sizeof(a));
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=i;j++)
		{
			cin>>a[i][j];
			a[i][j]+=a[i][j-1];
		}
	}
	ll ans=-inf;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=i;j++)
		{
			ll sum=0;
			for(int k=1;k<=n-i+1;k++)
			{
				sum+=a[i+k-1][j+k-1]-a[i+k-1][j-1];
				if(k<K)continue;
				if(k>K*2)break;
				ans=max(ans,sum/(k*(k+1)/2));
			}
		}
	}
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=i;j++)
		{
			ll sum=0;
			for(int k=1;k<=j&&k<=i-j+1;k++)
			{
				sum+=a[i-k+1][j]-a[i-k+1][j-k];
				if(k<K)continue;
				if(k>K*2)break;
				ans=max(ans,sum/(k*(k+1)/2));
			}
		}
	}
	cout<<ans<<'\n';
	return 0;
}

#include <bits/stdc++.h>
using namespace std;

using ll=long long;
const ll inf=0x3f3f3f3f3f3f3f3f;
const int N=705;
ll a[N][N];
int main()
{
	ios::sync_with_stdio(0);cin.tie(0);
	int n,K;cin>>n>>K;
    memset(a,0,sizeof(a));
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=i;j++)
		{
			cin>>a[i][j];
			a[i][j]+=a[i][j-1];
		}
	}
	ll ans=-inf;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=i;j++)
		{
			ll sum=0;
			for(int k=1;k<=n-i+1;k++)
			{
				sum+=a[i+k-1][j+k-1]-a[i+k-1][j-1];
				if(k<K)continue;
				if(k>K*2)break;
				ans=max(ans,sum/(k*(k+1)/2));
			}
		}
	}
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=i;j++)
		{
			ll sum=0;
			for(int k=1;k<=j&&k<=i-j+1;k++)
			{
				sum+=a[i-k+1][j]-a[i-k+1][j-k];
				if(k<K)continue;
				if(k>K*2)break;
				ans=max(ans,sum/(k*(k+1)/2));
			}
		}
	}
	cout<<ans<<'\n';
	return 0;
}