#include <bits/stdc++.h>
#define MAXN 1000

int v[1 + MAXN][1 + MAXN];
long long s[1 + MAXN][1 + MAXN];
long long diag[1 + MAXN][1 + MAXN];
long long oriz[1 + MAXN][1 + MAXN];
long long vert[1 + MAXN][1 + MAXN];
int main(){
    FILE*fi,*fo;
    fi=fopen("ferma2.in","r");
    fo=fopen("ferma2.out","w");

    int n, k;
    long long sum = 0;
    fscanf(fi,"%d%d", &n, &k);
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= i; j++){
            int x;
            fscanf(fi,"%d", &x);
            diag[i][j] = diag[i - 1][j - 1] + x;
            oriz[i][j] = oriz[i][j - 1] + x;
            vert[i][j] = vert[i - 1][j] + x;
            v[i][j] = x;
            sum += x;
        }
    }
    int nlat = n - k;
    for(int i = 1; i <= nlat; i++)
        for(int j = 1; j <= i; j++)
            s[nlat][1] += v[i][j];
    for(int i = nlat; i <= n; i++){
        if(i != nlat)
            s[i][1] = s[i - 1][1] + oriz[i][nlat] - diag[i - 1][nlat];
        for(int j = 2; j <= i; j++)
            s[i][j] = s[i][j - 1] - (vert[i][j - 1] - vert[i - nlat][j - 1]) + (diag[i][j + nlat - 1] - diag[i - nlat][j - 1]);
    }
    long long min = 1000000000000000000;
    for(int i = nlat; i <= n; i++)
        for(int j = 1; j + nlat - 1 <= i; j++)
            if(s[i][j] < min)
                min = s[i][j];
    fprintf(fo,"%lld", sum - min);
    fclose(fi);
    fclose(fo);
    return 0;
}