#include<bits/stdc++.h>
using namespace std;
int n,K,a[2001005],pr[2001005],lr[2001005],t[2001006],p = 1,k = 1,w;
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cin>>n>>K;
for(int i = 1;i < n; ++i)
{
int l = (i * (i + 1)) / 2 + 1,r = l + 1;
for(int j = p;j <= k; ++j)
{
pr[l] = lr[r] = j;
l = r;
r++;
}
p = (i * (i + 1)) / 2 + 1,k = p + i;
}
cin>>a[1];
t[1] = 1;
w = a[1];
int x = (n * (n + 1)) / 2;
for(int i = 2;i <= x; ++i)
{
cin>>a[i];
if(!lr[i] || !pr[i])
t[i] = max(t[lr[i]],t[pr[i]]) + 1;
else
t[i] = t[lr[i]] + t[pr[i]] - t[pr[lr[i]]] + 1;
if(t[i] <= K) w = min(w,a[i]);
}
cout<<w;
return 0;
}