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#include <bits/stdc++.h>


#define FOR(i, a, b) for(int i = a; i<b; ++i)
#define FR(i, a, b) for(int i = a; i>=b; --i)
#define _upgrade cin.tie(0); ios_base::sync_with_stdio(0)
#define pb push_back
#define mp make_pair
#define INF 1e9

using namespace std;

typedef long long ll;
typedef double db;
typedef unsigned long long ull;
typedef pair<int, int> iPair;


const int MAX = 1e6 +1;
const int MOD = 1e9 +7;




int dp[2001][2001], tab[2001][2001];

int main()
{
    _upgrade;
    int n, k, ans = INF;
    cin>>n>>k;
    FOR(i, 0, n)
        FOR(j, 0, i+1)
            cin>>tab[i][j];

    FOR(i, 0, n)
        FOR(j, 0, i+1)
        {
            int a, b, c;
            if(j == i)
                a = 0;
            else
                a = dp[i-1][j];
            if(j == 0)
                b = 0;
            else
                b = dp[i-1][j-1];
            if(i <= 1 || j == 0)
                c = 0;
            else
                c = dp[i-2][j-1];
            dp[i][j] = a + b - c + 1;
            if(dp[i][j] <= k)
                ans = min(ans, tab[i][j]);

        }
    cout<<ans<<"\n";
}