#include <bits/stdc++.h>

using namespace std;
ifstream f("ferma2.in");
ofstream g("ferma2.out");

const int NMax = 1003;

int n,k;
int a[NMax][NMax],c[NMax][NMax],l[NMax][NMax],d[NMax][NMax],d2[NMax][NMax];

int trian(int i,int j,int lat){
    int s = 0;
    s += c[n][j - 1];

    s += l[i + lat][j];

    s += d[i + lat - 1][j + lat];

    if(i - 2 >= 1)
        s -= d2[i - 2][j - 1];

    return s;
}
int main()
{
    f >> n >> k;
    int lat = n - k;
    for(int i = 1; i <= n; ++i){
        for(int j = 1; j <= i; ++j){
            f >> a[i][j];

            if(i == j)
                c[i][j] = c[i][j - 1] + a[i][j];
            else
                c[i][j] = c[i - 1][j] + c[i][j - 1] - c[i - 1][j - 1] + a[i][j];
        }
    }

    for(int i = n; i >= 1; --i){
        for(int j = i; j >= 1; --j){
            if(i == j)
                l[i][j] = l[i + 1][j] + a[i][j];
            else
                l[i][j] = l[i + 1][j] + l[i][j + 1] - l[i + 1][j + 1] + a[i][j];
        }
    }
    for(int i = 1; i <= n; ++i){
        for(int j = i; j >= 1; --j){
            if(i == j)
                d[i][j] = d[i - 1][j - 1] + a[i][j];
            else{

                if(j == 1){
                    d[i][j] = d[i][j + 1] + a[i][j];
                }else
                    d[i][j] = d[i][j + 1] + d[i - 1][j - 1] - d[i - 1][j] + a[i][j];
            }
        }
    }
    for(int i = 1; i <= n; ++i){
        int start = i;
        for(int j = 1; j <= n - i + 1; ++j){

            if(j == 1){
                d2[start][j] = d2[start - 1][j] + a[start][j];
            }else{
                d2[start][j] = d2[start - 1][j - 1] + d2[start - 1][j] - d2[start - 2][j - 1] + a[start][j];
            }
            start++;
        }
    }
    int ans = 0;
    for(int i = 1; i <= n - lat + 1; ++i){
        for(int j = 1; j <= i; ++j){
            ans = max(ans,trian(i,j,lat));
        }
    }

    g << ans << '\n';
    return 0;
}