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#include <iostream>
#include <vector>

using namespace std;

int T(int n)
{
    return n * (n + 1) / 2;
}

int main()
{
    ios_base::sync_with_stdio(0);
    int n, k;
    cin >> n >> k;
    vector< vector<int> > a(n);
    for (int i = 0; i < n; ++i)
    {
        for (int j = 0; j < i + 1; ++j)
        {
            int x;
            cin >> x;
            a[i].push_back(x);
        }
    }
    int odp = 2019;
    int pod = 0;
    for (int i = n - 1; i >= 0; --i)
    {
        for (int j = 0; j < i + 1; ++j)
        {
            int le = j, pr = i - j;
            if (T(n) - pod - T(le) - T(pr) <= k)
                odp = min(odp, a[i][j]);
        }
        pod += i + 1;
    }
    cout << odp;
    return 0;
}