#include <cstdio>
#include <cctype>

using namespace std;

const int BUFF_SIZE = (1 << 17);

FILE *fin;
int buffp = BUFF_SIZE - 1;
char buff[BUFF_SIZE];

inline void next_char() {
  if (++buffp == BUFF_SIZE) {
    fread(buff, 1, BUFF_SIZE, fin);
    buffp = 0;
  }
}

inline int get_num() {
  int num = 0;
  while (isdigit(buff[buffp]) == 0)
    next_char();
  while (isdigit(buff[buffp])) {
    num = num * 10 + buff[buffp] - '0';
    next_char();
  }
  return num;
}

const int MAXN = 1000;

int diag[MAXN + 1][MAXN + 1], left[MAXN + 1][MAXN + 1], up[MAXN + 1][MAXN + 1], tri[MAXN + 1][MAXN + 1];

inline int minimum(int a, int b) {
  if (a < b)
    return a;
  return b;
}

int main() {
    FILE *fout;
    int n, k, i, j, side, sum, minsum, num;
    fin = fopen("ferma2.in", "r");
    n = get_num(); k = get_num();
    sum = 0;
    for (i = 1; i <=n; ++i)
      for (j = 1; j <= i; ++j) {
        sum += (num = get_num());
        diag[i][j] = diag[i - 1][j - 1] + num;
        left[i][j] = left[i][j - 1] + num;
        up[i][j] = up[i - 1][j] + num;
      }
    fclose(fin);
    side = n - k;
    for (i = 1; i <= side; ++i)
      tri[1][1] += up[side][i];
    minsum = tri[1][1];
    for (i = 2; i + side - 1 <= n; ++i) {
      tri[i][1] = tri[i - 1][1] - diag[i + side - 2][side] + left[i + side - 1][side];
      minsum = minimum(minsum, tri[i][1]);
      for (j = 2; j <= i; ++j) {
        tri[i][j] = tri[i][j - 1] + diag[i + side - 1][j + side - 1] - diag[i - 1][j - 1] - up[i + side - 1][j - 1] + up[i - 1][j - 1];
        minsum = minimum(minsum, tri[i][j]);
      }
    }
    fout = fopen("ferma2.out", "w");
    fprintf(fout, "%d\n", sum - minsum);
    fclose(fout);
    return 0;
}