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#include <bits/stdc++.h>

typedef long long int ll;

using namespace std;

int main()
{
    ios_base::sync_with_stdio(false);
    
    int n, k;
    cin >> n >> k;
    
    int result = numeric_limits<int>::max();
    for (int h = 1; h <= n; ++h)
    {
        for (int i = 1; i <= h; ++i)
        {
            int age;
            cin >> age;
            
            int removed = i * (h - i + 1);
            if (removed <= k)
                result = min(result, age);
        }
    }
    
    cout << result << "\n";

    return 0;
}