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#include <bits/stdc++.h>

using namespace std;

#define PB push_back
#define SZ(x) int((x).size())
#define REP(i, n) for(int i=0,_=(n);i<_;++i)
#define FOR(i, a, b) for(int i=(a),_=(b);i<=_;++i)
#define FORD(i, a, b) for(int i=(a),_=(b);i>=_;--i)

#ifdef DEBUG
#define DEB(x) (cerr << x)
#else
#define DEB(x)
#endif

typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;

const int INF = 1e9 + 9;

void inline one() {
    int n, k;
    cin >> n >> k;
    int best = INF;
    REP(i, n) {
        FOR(j, 0, i) {
            int x;
            cin >> x;
            int required = (j + 1) * (i - j + 1);
            if (k >= required) {
                best = min(best, x);
            }
        }
    }
    cout << best << "\n";
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    //int z; cin >> z; while(z--)
    one();
}