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#include <bits/stdc++.h>
using namespace std;

#define endl '\n'
#define L long long
#define MP make_pair
#define REP(i, n) for(int i = 0; i < n; ++i)
#define REPR(i, n) for(int i = n - 1; i >= 0; --i)
#define FOR(i, a, b) for(int i = a; i < b; ++i)
#define FORR(i, a, b) for(int i = b - 1; i >= a; --i)
#define EB emplace_back
#define ST first
#define ND second
#define S size()
#define RS resize

using VI = vector<int>;
using VVI = vector<VI>;
using PI = pair<int, int>;
using VPI = vector<PI>;
using VVPI = vector<VPI>;
using VL = vector<L>;
using VVL = vector<VL>;
using VB = vector<bool>;
using VC = vector<char>;

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n, k;
    cin >> n >> k;
    VVI w(n, VI(n));
    REP(i, n)
        REP(j, i + 1)
            cin >> w[i][j];
    VVI dp(n, VI(n));
    REP(i, n)
        dp[i][0] = dp[i][i] = i + 1;
    FOR(i, 2, n)
        FOR(j, 1, i)
            dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j] - dp[i - 2][j - 1] + 1;
    int wyn = 2020;
    REP(i, n)
        REP(j, i + 1)
            if (dp[i][j] <= k)
                wyn = min(wyn, w[i][j]);
    cout << wyn;
}