#include<bits/stdc++.h>
using namespace std;
int year, n, k, result = 2020;
int score (int x, int y)
{
    int l, r, ret = 0;
    l = x, r = x;
    while (y >= 0)
    {
        ret += r - l + 1;
        y--;
        l = max(0, l - 1);
        r = min(r, y);
    }
    return ret;
}
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> k;
    for (int i = 0; i < n; ++i)
        for (int j = 0; j <= i; ++j)
        {
            cin >> year;
            if (score (j, i) <= k) result = min(result, year);
        }
    cout << result;
    return 0;
}