#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2005;
int n, k;
vector<int> wina[MAXN];
vector<int> DP[MAXN];
int main()
{
scanf("%d%d", &n, &k);
int res = 1e9;
for(int i = 1; i <= n; i++) {
for(int j = 0; j < i; j++) {
int a;
scanf("%d", &a);
wina[i].push_back(a);
if(i == 1)
DP[i].push_back(1);
else if(j == 0)
DP[i].push_back(DP[i-1][0] + 1);
else if(j == i - 1)
DP[i].push_back(DP[i-1][j-1] + 1);
else
DP[i].push_back(DP[i-1][j-1] + DP[i-1][j] - DP[i-2][j-1] + 1);
if(DP[i][j] <= k)
res = min(res, wina[i][j]);
// printf("%d ", DP[i][j]);
}
// printf("\n");
}
printf("%d", res);
}