#include<fstream>
using namespace std;
int a[1003][1003],c[1003][1003];
int main(void){
    ifstream fin("ferma2.in");
    ofstream fout("ferma2.out"); 
    int i,j,d,o,v,pozi,pozj,s=0,n,k,k1,sum,max=1000000000,sumel=0;
    fin>>n>>k;
    for(i=1;i<=n;++i)
      for(j=1;j<=i;++j){ fin>>a[i][j]; sumel+=a[i][j]; } fin.close();
    for(i=1;i<=n;++i)
      for(j=1;j<=i;++j)c[i][j]=a[i][j]+c[i][j-1];  
    for(k1=1;k1<=n-k+1;++k1)  
      for(i=1;i<n-k+1;++i){
        s=0; sum=0;
        for(j=i;j<=i+k-1;++j){
          s++;                    
          sum+=c[i+k1+s-2][j]-c[i+k1+s-2][j-s];
          }
       if(sum<max)max=sum;
       }                       
  fout<<(sumel-max);                                                     
fout.close();             
 return 0;   
}