#include <stdio.h>

using namespace std;
const int NMAX = 1000, INF = 1e9;

int linSum[NMAX + 1][NMAX + 1], colSum[NMAX + 1][NMAX + 1], diagSum[NMAX + 1][NMAX + 1];
void readAndInitSum(int &n, int &k, int &sum);

int main()
{
    int n, k, i, j, sum, sumTr, sumTrBeg, minSumTr;
    readAndInitSum(n, k, sum);

    k = n - k;
    sumTrBeg = 0;
    for(i = 1; i <= k - 1; i++)
            sumTrBeg += linSum[i][i];

    minSumTr = sumTrBeg - diagSum[i - 1][k] + linSum[i][k];
    for (i; i <= n; i++)
    {
        sumTrBeg = sumTrBeg - diagSum[i - 1][k] + linSum[i][k];
        if (sumTrBeg < minSumTr)
            minSumTr = sumTrBeg;
        sumTr = sumTrBeg;
        for (j = 2; j <= i - k + 1; j++)
        {
            sumTr = sumTr - colSum[i][j - 1] + colSum[i - k][j - 1] + diagSum[i][j + k - 1] - diagSum[i - k][j - 1];
            if(minSumTr > sumTr)
                minSumTr = sumTr;
        }
    }
    sum -= minSumTr;

    FILE *fout = fopen("ferma2.out", "w");
    fprintf(fout, "%d", sum);
    fclose(fout);


    return 0;
}

void readAndInitSum(int &n, int &k, int &sum)
{
    int val;
    sum = 0;
    FILE *fin = fopen("ferma2.in", "r");
    fscanf(fin, "%d%d", &n, &k);
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= i; j++)
        {
            fscanf(fin, "%d", &val);
            sum += val;
            colSum[i][j] += colSum[i - 1][j] + val;
            linSum[i][j] += linSum[i][j - 1] + val;
            diagSum[i][j] += diagSum[i - 1][j - 1] + val;
        }
    fclose(fin);
}