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#include <bits/stdc++.h>
using namespace std;
#define VAR(n,v) decltype(v) n=(v)
#define REP(i,n) for(int i=1; i<=(n); ++i)
#define FOR(i,a,b) for(VAR(i,a); i!=(b); ++i)
#define FORE(it,t) FOR(it,t.begin(),t.end())
typedef vector<int> vi;
#define pb push_back
typedef pair<int,int> pii;
#define mp make_pair
#define st first
#define nd second
typedef long long ll;
#define INF 1000000001
#define sz size()
#define ALL(t) (t).begin(),(t).end()
#define SC(a) scanf("%d", &a)
#define GET(a) int a; SC(a)
#define ISDEBUG 0
#define dprintf(...) if(ISDEBUG) \
	{printf("\033[31m"); printf(__VA_ARGS__); printf("\033[0m");}
template <class It> void dptab(It b, It e, const char* f="%d ")
	{if(ISDEBUG) {for(It it=b; it!=e; ++it) dprintf(f, *it); dprintf("\n"); }}

int main() {
	GET(n);
	GET(k);
	int min_year = INF;
	REP(i,n) {
		REP(j,i) {
			GET(year);
			int above = j*(i-j+1);
			if (above <= k) {
				min_year = min(year, min_year);
			}
			dprintf("(%d, %d) %d: %d\n", i, j, year, above);
		}
	}
	printf("%d\n", min_year);
}