#include <bits/stdc++.h>
using namespace std;
ifstream f("ferma2.in");
ofstream g("ferma2.out");
const int nMax = 1003;
int lin[nMax][nMax];
int col[nMax][nMax];
int diag[nMax][nMax];
int n , k , x, total;
inline void Solve() {
    int lim = n - k , sumlin = 0, sol, suma = 0;
    for(int i = 1; i <= lim; i++) {
        sumlin += lin[i][i];
    }
    sol = suma = sumlin;
    for(int i = 2; i <= k + 1; i++) {


        suma = sumlin = sumlin += lin[i + lim - 1][lim] - diag[i + lim - 2][lim];
        sol = min(sol, suma);
        for(int j = 2; j <= i; j++) {

            suma = suma - (col[i + lim - 1][j - 1] - col[i - 1][j - 1]) +
                         (diag[i + lim - 1][j + lim - 1] - diag[i - 1][j - 1]);
            sol = min(sol, suma);
        }

    }
    g<< total - sol << "\n";
}
int main()
{

    f >> n >> k;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= i; j++) {
            f >> x;
            total += x;
            lin[i][j] = lin[i][j - 1] + x;
            col[i][j] = col[i - 1][j] + x;
            diag[i][j] = diag[i - 1][j - 1] + x;
        }
    }
    Solve();
    return 0;
}