#include <bits/stdc++.h>

#define NMax 1001
#define INF 0x3f3f3f3f
using namespace std;
ifstream f("ferma2.in");
ofstream g("ferma2.out");

int n,w,s;
int a[NMax][NMax];
int dp[4][NMax][NMax];

int main()
{
    f >> n >> w;
    for(int i = 1; i <= n; ++i){
        for(int j = 1; j <= i; ++j){
            f >> a[i][j];
            dp[1][i][j] = a[i][j];
            s += a[i][j];
        }
    }
    w = n - w;
    for(int k = 2; k < w; ++k){
        int E = 2;
        for(int i = k; i <= n; ++i){
            for(int j = 1; j <= i - k + 1; ++j){
                dp[E][i][j] = a[i][j] + dp[E - 1][i][j + 1] + dp[E - 1][i - 1][j] - dp[E - 2][i - 1][j + 1];
            }
        }
        for(int i = 1; i <= n; ++i){
            for(int j = 1; j <= i; ++j){
                dp[E - 2][i][j] = dp[E - 1][i][j];
                dp[E - 1][i][j] = dp[E][i][j];
            }
        }
    }
    int E = 2,ans = INF;
    for(int i = w; i <= n; ++i){
        for(int j = 1; j <= i - w + 1; ++j){
            dp[E][i][j] = a[i][j] + dp[E - 1][i][j + 1] + dp[E - 1][i - 1][j] - dp[E - 2][i - 1][j + 1];
            ans = min(dp[E][i][j],ans);
        }
    }
    g << s - ans << '\n';
    return 0;
}