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#include<bits/stdc++.h>

using namespace std;

#define PB push_back
#define MP make_pair
#define F first
#define S second
#define ALL(x) (x).begin(),(x).end()
#define SIZE(x) (int)(x).size()
#define CLEAR(tab) memset(tab, 0, sizeof(tab))
#define REP(x, n) for(int x = 0; x < (n); x++)
#define FOR(x, b, e) for(int x = (b); x <= (e); x++)
#define FORD(x, b, e) for(int x = (b); x >= (e); x--)
#define VAR(v, n) __typeof(n) v = (n)
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define DEBUG(fmt, ...) fprintf(stderr, fmt, ##__VA_ARGS__)

typedef long long int LL;
typedef pair<int,int> PII;
typedef vector<int> VI;

const int MXN = 2010;
const int C = 262144;
const int INF = 1000000001;

int a[MXN][MXN];
int n, k;
int cnt[MXN][MXN];

void test() {
	scanf("%d %d", &n, &k);
//	scanf("%d", &k);
	FOR(i, 1, n)
		FOR(j, 1, i)
			scanf("%d", &a[i][j]);
	int res = a[1][1];
	FOR(i, 1, n)
		FOR(j, 1, i)
			cnt[i][j] = 1 + cnt[i - 1][j];
	FOR(i, 1, n)
		FOR(j, 1, i)
			cnt[i][j] += cnt[i - 1][j - 1];

	FOR(i, 1, n)
		FOR(j, 1, i)
			if(cnt[i][j] <= k)
				res = min(res, a[i][j]);
	printf("%d\n", res);
}

int main() {
//	int te = 1;
//	scanf("%d", &te);
//	while(scanf("%d", &n) != EOF)
		test();
	return 0;
}