1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
#include <bits/stdc++.h>

typedef unsigned short us;
typedef short s;
typedef unsigned long ul;
typedef long l;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;

const l INF = 1e9 + 9;
const l MOD = 1e9 + 7;
const l PRIME = 200003;
const ll L_INF = 1e18 + 1;
const double EPS = 10e-9;

#define FOR(x, y, z) for (l z = x; z < y; z++)
#define FORE(x, y, z) for (l z = x; z <= y; z++)
#define FORD(x, y, z) for (l z = x; z > y; z--)
#define FORDE(x, y, z) for (l z = x; z >= y; z--)
#define REP(x, y) for (l y = 0; y < x; y++)

#define PF push_front
#define POF pop_front
#define PB push_back
#define POB pop_back
#define MP make_pair
#define FS first
#define SC second

using namespace std;

l height, num_moves, res = INF;
l prefix_sum[2001005];
vector<l> bottles[2015];

fstream input, output;

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);

	cin >> height >> num_moves;

	FORE(1, height, i)
	{
		FORE(1, i, j)
		{
			l a;
			cin >> a;

			bottles[i].PB(a);
		}
	}

	prefix_sum[1] = 1;
	prefix_sum[2] = 2;
	prefix_sum[3] = 2;

	FORE(3, height, i)
	{
		FORE(1, i, j)
		{
			l pos = (((i - 1) * i) / 2) + j;

			if (j == 1)
				prefix_sum[pos] = prefix_sum[(((i - 2) * (i - 1)) / 2) + 1] + 1;

			else if (j == i)
				prefix_sum[pos] = prefix_sum[(((i - 1) * i) / 2)] + 1;

			else
			{
				prefix_sum[pos] = prefix_sum[((((i - 2) * (i - 1)) / 2) + j - 1)] + prefix_sum[((((i - 2) * (i - 1)) / 2) + j)] - prefix_sum[((((i - 3) * (i - 2)) / 2) + j - 1)] + 1;
			}
		}
	}

	FORE(1, height, i)
	{
		FORE(1, i, j)
		{
			l pos = (((i - 1) * i) / 2) + j;

			if (prefix_sum[pos] <= num_moves)
				res = min(res, bottles[i][j - 1]);
		}
	}

	cout << res << "\n";
}