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