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#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <set>
#include <map>
#include <string>
#include <queue>
#include <stack>
#include <unordered_map>
using namespace std;

typedef long long int LL;
typedef long double LD;
typedef vector<int> VI;
typedef vector<LL> VLL;
typedef vector<LD> VLD;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;

const int INF = 1000000001;
const LD EPS = 10e-9;

#define FOR(x, b, e) for(int x = b; x <= (e); ++x)
#define FORD(x, b, e) for(int x = b; x >= (e); --x)
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define MP make_pair
#define PB push_back
#define ST first
#define ND second
#define abs(a) ((a)<0 ? -(a) : (a))
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) < (b) ? (a) : (b))

int main()
{
    ios_base::sync_with_stdio(0);

    int n, k, a;
    while(cin >> n >> k)
    {
        int res = 10000;
        for(int i = 1; i <= n; ++i)
        {
            for(int j = 1; j <= i; ++j)
            {
                cin >> a;
                //cout << a << endl;

                const int reqMoves = j * (1+i-j);
                if(reqMoves <= k && a < res)
                {
                    res = a;
                }
            }
            //cout << endl;
        }

        cout << res << endl;
    }

    return 0;
}