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#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

vector<int> shelf[2001];




bool isThere(int hInd, int rInd) {

    if(hInd < 0 || rInd < 0) {
        return false;
    }

    if(rInd > hInd) {
        return false;
    }

    return true;
}

void fillDep(int n) {

    for(int i = 0; i < n; i++) {
        for(int j = 0; j <= i; j++)
        {
            int toRem = 0;

            if(isThere(i-1, j-1)) {
                toRem += shelf[i-1][j-1] + 1;
            }

            if(isThere(i-1, j) ) {
                toRem += shelf[i-1][j] + 1;
            }

            if(isThere(i-2, j-1) ) {
                toRem -= shelf[i-2][j-1] + 1;
            }

            shelf[i].push_back(toRem);
        }
    }
}

void testFil(int n) {

    for(int i = 0; i < n; i++) {
        for(int j = 0; j <= i; j++) {
            cout << shelf[i][j] << " ";
        }
        cout << "\n";
    }
}

int main() {

    ios_base::sync_with_stdio(0);

    int n, k;

    cin >> n >> k;

    fillDep(n);
    
    int kings = 2020;

    for(int i=0; i<n; i++)
    {
        for(int j=0; j <= i; j++) {
            int year;
            cin >> year;

            int toReach = shelf[i][j];
            
            if(toReach < k) {
                kings = min(kings, year);
            }
        }
    }

    cout << kings << "\n";


    return 0;
}