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#include <cstdio>
#include <utility>
#include <queue>
#include <set>
#include <list>
#include <map>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
using namespace std;
typedef vector<int> VI;
typedef long long LL;
#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 FOREACH(i,c) for(VAR(i,(c).begin());i!=(c).end();++i)
#define PB push_back
#define ST first
#define ND second
#define MP make_pair
#define PII pair<int, int>

bool Valid(int i, int j, int n) {
    return i >= 0 && i < n && j >= 0 && j <= i;
}

int main() {
    int n, k;
    scanf("%d %d", &n, &k);
    vector<vector<int>> wines(n);
    vector<vector<int>> A(n);
    REP(i, n) {
        REP(j, i+1) {
            int year;
            scanf("%d", &year);
            wines[i].push_back(year);
            A[i].push_back(0);
        }
    }
    int best = wines[0][0];
    REP(i, n) {
        REP(j, i+1) {
            int res = 1;
            // std::cout << i << " " << j  << " " << res << ",";
            if (Valid(i-1, j-1, n))
                res += A[i-1][j-1];
            // std::cout << i << " " << j  << " " << res << ",";
            if (Valid(i-1, j, n))
                res += A[i-1][j];
            // std::cout << i << " " << j  << " " << res << ",";
            if (Valid(i-2, j-1, n))
                res -= A[i-2][j-1];
            // std::cout << i << " " << j  << " " << res << ",";
            A[i][j] = res;
            if (res <= k)
                best = min(best, wines[i][j]);
            // cout << A[i][j] << " ";
        }
        // cout << endl;
    }
    printf("%d\n", best);
    return 0;
}