#include <iostream>
#include <cstdio>
#define MAXN 1050

using namespace std;

int n, k, dif, tot, a[MAXN][MAXN];
int diags[MAXN][MAXN], lins[MAXN][MAXN];

void read()
{
    scanf("%d %d", &n, &k);
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= i; j++)
            scanf("%d", &a[i][j]);
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= i; j++)
    {
        tot += a[i][j];
        diags[i-j+1][j] = a[i][j] + diags[i-j+1][j-1];
        lins[i][j] = a[i][j] + lins[i][j-1];
    }
    dif = n-k;
}

void solve()
{
    int minim = 0x3f3f3f3f;
    for (int col = 1; col <= n; col++) {
        int crt = 0;
        for (int j = 1; j <= dif; j++)
            crt += lins[col+j-1][col+j-1] - lins[col+j-1][col-1];
        for (int lin = col; lin <= n - dif+1; lin++) {
            if (crt < minim) minim = crt;
            crt += lins[lin+dif][col+dif-1] - lins[lin+dif][col-1];
            crt -= diags[lin-col+1][col+dif-1] - diags[lin-col+1][col-1];
        }
    }
    printf("%d", tot-minim);
}

int main()
{
    freopen("ferma2.in", "r", stdin);
    freopen("ferma2.out", "w", stdout);

    read();
    solve();

    return 0;
}