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#include<bits/stdc++.h>

using namespace std;

int main()
{
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	
	int n,k;
	cin >> n >> k;
	
	int ile = n*(n+1)/2;
	
	vector<int> a(ile+3);
	a[0] = 4e5;
	for(int i=1; i<=ile; ++i) cin >> a[i];
	
	vector<int> ileStarych(ile+3, -123123);
	
	ileStarych[1] = 1;
	ileStarych[2] = 2;
	ileStarych[3] = 2;
	
	int indeks = 4;
	for(int i=3; i<=n; ++i) 
	{
		int dod = i-2;
		ileStarych[indeks] = i;
		ileStarych[indeks+i-1] = i;
		
		for(int j=1; j<=(i/2); ++j)
			ileStarych[indeks+j] = ileStarych[indeks+j-1] + dod, dod -= 2;
			
		int js = (i/2)+1;
		dod = i-2;
		
		for(int j=i-2; j>=js; --j)
			ileStarych[indeks+j] = ileStarych[indeks+j+1] + dod, dod -= 2;
			
		indeks += i;
	}
	
	int res = 4e5;
	for(int i=1; i<=ile; ++i)
		if(res > a[i] && ileStarych[i] <= k) res = a[i];
		
	cout << res << '\n';
	
	return 0;
}