#include <iostream>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int n, k;
    cin >> n >> k;
    int total = n * (n + 1) / 2;
    int row = 1, col = 1;
    int year, needed;
    int min_year = 9999;
    for (int i = 0; i < total; i++) {
        cin >> year;
        needed = col * (row - col + 1);

        if (needed <= k && year < min_year) {
            min_year = year;
        }

        if (col == row) {
            row++;
            col = 1;
        } else {
            col++;
        }
    }
    cout << min_year << "\n";

    return 0;
}