#include <bits/stdc++.h>
using namespace std;
#define N 2000
int lata[N][N];
int kroki[N][N];
int main() {
int n, k;
scanf("%d %d", &n, &k);
int mn = INT_MAX;
int j = 1;
for (int i = 0; i < n; i++) {
for (int l = 0; l < j; l++) {
scanf("%d", &(lata[i][l]));
}
j++;
}
j = 2;
kroki[0][0] = 1;
for (int i = 1; i < n; i++) {
for (int l = 0; l < j; l++) {
if (l <= j/2) {
kroki[i][l] = kroki[i - 1][l] + l + 1;
}
else {
kroki[i][l] = kroki[i][j - l - 1];
}
}
j++;
}
j = 1;
for (int i = 0; i < n; i++) {
for (int l = 0; l < j; l++) {
if (kroki[i][l] <= k && lata[i][l] != 0) {
mn = min(mn, lata[i][l]);
}
}
j++;
}
printf("%d", mn);
return 0;
}
/*
5 7
1999
2019 2010
850 1500 1600
900 900 710 900
1000 800 600 800 1000
*/