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#include<bits/stdc++.h>
#define ALL(X)        X.begin(),X.end()
#define FOR(I,A,B)    for(int I = A; I <= B; I++)
#define FORW(I,A,B)   for(int I = A; I < B;  I++)
#define FORD(I,A,B)   for(int I = A; I >= B; I--)
#define CLEAR(X)      memset(X,0,sizeof(X))
#define SIZE(X)       int(X.size())
#define CONTAINS(A,X) (A.find(X) != A.end())
#define PB            push_back
#define MP            make_pair
#define X             first
#define Y             second
using namespace std;

typedef signed long long slong;
typedef long double ldouble;
const slong INF = 1000000100;
const ldouble EPS = 1e-9;

const int MAXN = 2020;
int DP[MAXN][MAXN];
int A[MAXN][MAXN];

int main() {
    while (true) {
        int N, K;
        if (scanf("%d %d", &N, &K) != 2) return 0;
        FOR(i,1,N) FOR(j,1,i) scanf("%d", &A[i][j]);
        FOR(i,1,N) FOR(j,1,i) DP[i][j] = 1 + DP[i-1][j-1] + DP[i-1][j] - DP[i-2][j-1];
//        FOR(i,1,5) { FOR(j,1,i) cout << DP[i][j] << " "; cout << endl; }
        int result = INF;
        FOR(i,1,N) FOR(j,1,i) if(DP[i][j] <= K) result = min(result, A[i][j]);
        printf("%d\n", result);
    }
}