#include<cstdio>
#include<vector>
#include<limits>
#include<algorithm>
using namespace std;
int main() {
int n, k;
scanf("%d %d", &n, &k);
vector<vector<int>> b(n);
for (int i = 0; i < n; ++i) {
b[i].resize(i + 1);
for (int j = 0; j <= i; ++j) {
scanf("%d", &b[i][j]);
}
}
int best = numeric_limits<int>::max();
int size = 0;
for (int i = 0; i < n && i < k; ++i) {
int steps = i + 1;
if (steps <= k) best = min(best, b[i][0]);
for (int j = 1; j <= i; ++j) {
steps += i - j - (j - 1);
if (steps <= k) best = min(best, b[i][j]);
}
}
printf("%d\n", best);
return 0;
}