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#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <list>
#include <ctime>
#include <sstream>
#include <queue>
#include <stack>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
using namespace std;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;
typedef short int sint;
#define FOR(x, b, e) for(int x=(b); x<=(e); ++x)
#define FORD(x, b, e) for(int x=((int)(b))-1; x>=(e); --x)
#define REP(x, n) for(int x=0; x<(n); ++x)
#define ALL(c) c.begin(),c.end()
#define SIZE(x) ((int)((x).size()))
#define PB push_back
#define ST first
#define ND second
#define DEBUG 1
#define debug(x) {if (DEBUG)cerr <<#x <<" = " <<x <<endl; }
#define debugv(x) {if (DEBUG) {cerr <<#x <<" = "; FOREACH(it, (x)) cerr <<*it <<", "; cout <<endl; }}
#define REMAX(a,b) (a)=max((a),(b));
#define REMIN(a,b) (a)=min((a),(b));
#define wez(n) int (n); scanf("%d",&(n));
#define wez2(n,m) int (n),(m); scanf("%d %d",&(n),&(m));

const int N = 2010;
int tab[N][N];
int wsk[N][N];
int best[N * N];
int n, k;

int main() {
	scanf("%d %d", &n, &k);
	// printf("%d, %d\n", n, k);
	REP(i, (n * (n + 1)) / 2 + 1) {
		best[i] = 2020;
	}
	for (int i = 1; i <=n; ++i) {
		wsk[i][1] = wsk[i][i] = i;
		for (int j=2; j <= (i + 1) / 2; ++j) {
			wsk[i][j] = wsk[i][i - j + 1] = wsk[i - 1][j] + wsk[i][j - 1] - wsk[i - 1][j - 1] + 1;
		}
		for (int j = 1; j<=i; ++j) {
			scanf("%d", &tab[i][j]);
			// printf("%d ", wsk[i][j]);
			REMIN(best[wsk[i][j]], tab[i][j]);
		}
		// printf("\n");
	}
	for (int i = 2; i <= (n * (n + 1)) /2; ++i) {
		REMIN(best[i], best[i - 1]);
	}
	printf("%d\n", best[k]);
	// printf("FINISHED\n");
	return 0;
}