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#include<bits/stdc++.h>
using namespace std;

int n,k;

vector < vector <int> > neighbours;

int wina[5000000];

pair <int,int> getCost[5000000];

void bfs()
{
    queue<int> tops;

    tops.push(1);

    while(!tops.empty())
    {
        int x = tops.front();

        tops.pop();

        if (neighbours[x].size() == 0)
            continue;

        getCost[neighbours[x][0]].first = getCost[x].first;
        getCost[neighbours[x][0]].second = getCost[x].second+1;

        getCost[neighbours[x][1]].first = getCost[x].first+1;
        getCost[neighbours[x][1]].second = getCost[x].second;

        tops.push(neighbours[x][0]);
        tops.push(neighbours[x][1]);
    }
}

int minValue()
{
    int result = wina[1];

    for (int i=1; i<(n-1)*(n-1); ++i)
    {
        if (k >= getCost[i].first*getCost[i].second - 1)
        {
            result = min(result, wina[i]);
        }
    }

    return result;
}

int main()
{
    scanf("%d%d",&n,&k);

    neighbours.resize(n*n+2);

    for(int row = 0; row < n; ++row)
    {
        for(int column=0; column < row+1; ++column)
        {
            int value;

            scanf("%d",&value);

            wina[(row)*(row+1)/2+column+1] = value;
        }
    }

    for (int row = 0; row < n-1; ++row)
    {
        for (int column = 0; column < row+1; ++column)
        {
            neighbours[(row)*(row+1)/2+column+1].push_back((row+1)*(row+2)/2+column+1);
            neighbours[(row)*(row+1)/2+column+1].push_back((row+1)*(row+2)/2+column+2);
        }
    }

    getCost[1] = {1,1};

    bfs();

    printf("%d", minValue());

    return 0;
}