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#include <cstdio>

int main(void)
{
    int n, k, l, c, y, kx, ks, a;

    a = 2020;

    scanf("%d%d", &n, &k);

    for (l = 1; l <= n; l++) {
        kx = l;
        ks = l;

        for (c = 0; c < l; c++) {
            scanf("%d", &y);

            if (kx <= k && y < a)
                a = y;

            ks -= 2;
            kx += ks;
        }
    }

    printf("%d\n", a);

    return 0;
}