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#include <iostream>

using namespace std;

int treeSize(int num) {
    return num < 1 ? 0 : ((1 + num) * num) / 2;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int n, k, year, result = 2020;

    cin >> n >> k;

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            cin >> year;
            int minBottles = treeSize(i) - treeSize(j - 1) - treeSize(i - j);
            if (minBottles <= k && result > year) {
                result = year;
            }
        }
    }
    cout << result << endl;
    return 0;
}