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#include <iostream>
#include <vector>
#include <unordered_map>
#include <limits>

#define DEBUG(x)
#define DEBUG2(x)
#define DEBUG3(x)

class DestackCounter
{
public:
    DestackCounter(int height)
        : cache_line_length(3),
          upper_cache_line(height),
          lower_cache_line(height),
          cache_line(height)
    {
        if (height < 3)
        {
            upper_cache_line.resize(3);
            lower_cache_line.resize(3);
            cache_line.resize(3);
        }

        DEBUG(std::cout << "upper_cache_line.size() = " << upper_cache_line.size() << std::endl;)

        upper_cache_line[0] = 1;

        lower_cache_line[0] = 2;
        lower_cache_line[1] = 2;

        cache_line[0] = 3;
        cache_line[1] = 4;
        cache_line[2] = 3;
        
    }

    int get_removal_cost(int row, int position)
    {
        if (row == 0)
            return 1;
        if (row == 1)
            return 2;

        if (row == cache_line_length)
            calculate_next_line();

        return cache_line[position];
    }

private:
    void calculate_next_line() {
        upper_cache_line = std::move(lower_cache_line);
        lower_cache_line = std::move(cache_line);
        cache_line.resize(upper_cache_line.size());
        cache_line_length += 1;

        for (int i = 0; i < cache_line_length; ++i) {
            cache_line[i] = get_prev(i) - get_prev_prev(i) + 1;
            DEBUG(std::cout << cache_line[i] << " ";)
        }
        DEBUG(std::cout << std::endl;)

        
    }

    int get_prev(int position) {
        if (position == 0)
            return lower_cache_line[0];
        if (position == cache_line_length - 1)
            return lower_cache_line[cache_line_length - 1 - 1];
        return lower_cache_line[position - 1] + lower_cache_line[position];
    }

    int get_prev_prev(int position) {
        if (position == 0)
            return 0;
        if (position == cache_line_length - 1)
            return 0;
        return upper_cache_line[position - 1];
    }

    int cache_line_length;
    std::vector<int> upper_cache_line;
    std::vector<int> lower_cache_line;
    std::vector<int> cache_line;
};

int main()
{
    int height = 0;
    int request_botels = 0;
    std::cin >> height >> request_botels;
    DEBUG(std::cout << "height = " << height << " requested_botels = " << request_botels << std::endl;)

    int best_year = std::numeric_limits<int>::max();
    DestackCounter destack_counter(height);
    for (int r = 0; r < height; ++r) {
        for (int p = 0; p <= r; ++p) {
            int year = 0;
            std::cin >> year;
            DEBUG2(std::cout << year << " ";)

            if (r < request_botels) {
                const int cost = destack_counter.get_removal_cost(r, p);
                if (cost <= request_botels && year < best_year) {
                    best_year = year;
                }
                DEBUG3(std::cout << "(" << r << ", " << p << ") -> best[" << cost << "] = " << year << std::endl;)
            }
        }
        DEBUG2(std::cout << std::endl;)
    }

    std::cout << best_year;
    return 0;
}