#include <algorithm>
#include <stdio.h>

int triangleSum(int n)
{
    return (1 + n) * n / 2;
}

void calculate(const int k, const int row, const int column, const int year, int& minYear)
{
    const int totalSum = triangleSum(row);
    const int leftSum = triangleSum(column - 1);
    const int rightSum = triangleSum(row - column);
    const int currentSum = totalSum - leftSum - rightSum;
    if (currentSum <= k) {
        minYear = std::min(year, minYear);
    }
}

int main()
{
    int n, k, year, minYear = 2020;
    scanf("%d %d\n", &n, &k);
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j <= i; ++j) {
            scanf("%d", &year);
            calculate(k, i + 1, j + 1, year, minYear);
        }
    }
    printf("%d\n", minYear);
    return 0;
}