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

long long t[5000005];
bool odw[5000005];

long long t2[5000005];

long long n,k,z = 100;

long long dod = 1,skok = 2;

long long skok2_start = 3, skok2;

long long indeks,wynik = INT_MAX;

void preprocessing()
{
    t[1] = 1;

    for(int i = 2, skok = 2; i <= (n * (n + 1)) / 2; i += skok, skok++)
        t[i] = skok, odw[i] = true;

    for(int i = 3, skok = 3; i <= (n * (n + 1)) / 2; i += skok, skok++)
        t[i] = skok - 1;

    for(int i = 2; i <= (n * (n + 1)) / 2; i++)
    {
        if(odw[i])
        {
            int poz = i;

            skok2 = skok2_start;

            for(int j = i + skok2; j <= (n * (n + 1)) / 2; skok2++, j += skok2)
            {
                if(!t[j])
                    t[j] = t[j - skok2] + t[poz];
            }

            skok2_start++;
        }
    }
}


int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> k;

    preprocessing();

        for(int i = 1; i <= (n * (n + 1)) / 2; i++)
        {
            cin >> t2[i];

            if(t[i] <= k)
            {
                if(t2[i] <= wynik)
                {
                    wynik = t2[i];
                    indeks = i;
                }
            }
        }

        cout << t2[indeks] << endl;
}