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#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <map>
#include <set>
#include <bitset>

using namespace std;

typedef unsigned long long LL;

#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define ABS(val) ((val) < 0 ? -(val) : (val))

#define FOR(x, b, e) for(int x = b; x <= (e); ++x)
#define FORD(x, b, e) for(int x = b; x >= (e); --x)
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define PB push_back
#define ST first
#define ND second

#define M 1000000007ULL

/* PA2019 "WIN" */

int main() {

	int n, k;
	scanf("%d %d\n", &n, &k);
	
	int res = 100000;

    REP(i, n) {
		REP(j, i+1) {
			int u;
			scanf("%d", &u);
			
			int r = (i - j + 1) * (j + 1);
			//printf("%d,", r);
			
			if (k >= r)
		      res = MIN(res, u);
		}
		//printf("\n");
	}
	
	printf("%d\n", res);
	
	

	
	


	return 0;
}