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#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for (int i = (a); i <= (b); ++i)
#define REPD(i,a,b) for (int i = (a); i >= (b); --i)
#define FORI(i,n) REP(i,1,n)
#define FOR(i,n) REP(i,0,int(n)-1)
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define SZ(x) int((x).size())
#define DBG(v) cerr << #v << " = " << (v) << endl;
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define fi first
#define se second

int a[2020][2020], t[2020][2020];

int main() {
	int n,k;
	int res = 2020;
	scanf("%d%d", &n, &k);
	FORI(i,n) {
		FORI(j,i) {
			scanf("%d", &a[i][j]);
		}
	}
	FORI(i,n) {
		FORI(j,i) {
			if (i >= 2) t[i][j] = t[i-1][j-1] + t[i-1][j] - t[i-2][j-1] + 1;
			else t[i][j] = 1;
			if (t[i][j] <= k) res = min(res, a[i][j]);
			//printf("%d -> %d\n", a[i][j], t[i][j]);
		}
	}
	printf("%d\n", res);
	return 0;
}