//#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define ll long long
#define ld long double
#define pi pair<int,int>
#define pd pair<ld,ld>
#define ft first
#define sd second
#define st first
#define nd second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define FOR(i,a,b) for(int i=(a); i<=(b);i++)
#define F(i,a,b) FOR(i,(a),(b)-1)
#define REV(i,a,b) for(int i=(a); i>=(b);i--)
#define VI vector<int>
#define VPI vector<pi>
#define VPD vector<pd>
#define PI 3.14159265
#define all(x) (x).begin(), (x).end()
#define sz(a) (int)((a).size())
#define int long long
template<class TH> void _dbg(const char *sdbg, TH h){cerr<<sdbg<<"="<<h<<"\n";}
template<class TH, class... TA> void _dbg(const char *sdbg, TH h, TA... a) {
while(*sdbg!=',')cerr<<*sdbg++;cerr<<"="<<h<<","; _dbg(sdbg+1, a...);
}
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
//mt19937 r(chrono::steady_clock::now().time_since_epoch().count());
//int rand_range(int a, int b)
//{
// assert(a<=b);
// return a+r()%(b-a+1);
//}
const long long K = 1000;
const long long KK = K*K;
const long long MIL = KK*K;
const long long INF = MIL*MIL;
const long long MOD = MIL+7;
const long long N = 2e3 + 10, M=10;
int tab[N][N];
int dp[N][N];
void solve(){
int n, k;
cin >> n >> k;
FOR(i, 1, n) {
FOR(j, 1, i){
cin >> tab[i][j];
}
}
dp[1][1] = 1;
int res = tab[1][1];
FOR(i, 2, n) {
FOR(j, 1, i){
dp[i][j] = 1 + dp[i - 1][j - 1] + dp[i - 1][j] - dp[i - 2][j - 1];
if (dp[i][j] <= k)
res = min(res, tab[i][j]);
// debug(i, j, dp[i][j]);
}
}
cout << res << "\n";
}
int32_t main()
{
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cerr.tie(0);
cout<<setprecision(9)<<fixed;
cerr<<setprecision(6)<<fixed;
int test = 1, f;
//cin>>test;
F(_test, 0, test){
//cout<<"Case #"<<_test + 1<<": ";
solve();
// if(_test == 1)
// return 0;
}
}