#include <iostream>
#include <vector>
using namespace std;
int main()
{
int levels, needed, year, index, min;
cin >> levels >> needed;
vector<vector<int> > bottles(levels);
for (int i = 0; i < levels; i++)
{
for (int j = 0; j <= i; j++)
{
cin >> year;
bottles[i].push_back(year);
}
}
min = bottles[0][0];
for (int i = 0; i < levels && i < needed; i++)
{
if (bottles[i][0] < min)
{
min = bottles[i][0];
}
}
for (int i = 0; i < levels && i < needed; i++)
{
index = bottles[i].size() - 1;
if (bottles[i][index] < min)
{
min = bottles[i][index];
}
}
for (int y = 0; y < levels; y++)
{
if (needed <= 0)
{
break;
}
for (unsigned int i = 0; i < bottles[y].size(); i++)
{
if (bottles[y][i] < min)
{
min = bottles[y][i];
}
needed--;
}
}
cout << min << endl;
return 0;
}