import bisect

n, m = map(int, input().rstrip().split())
k_pts = int(input())
pts_list = []
for i in range(n - 1):
    bisect.insort(pts_list, int(input()))

def solve(k_pts, m, pts_list):
    for i in range(len(pts_list)):
        x = pts_list[i]
        del pts_list[i]
        counter = 0
        for j in range(len(pts_list)):
            if counter == m:
                break
            elif len(pts_list) - j - 1 <= bisect.bisect_right(pts_list, k_pts + x - pts_list[- j - 1]):
                return x
            else:
                counter += 1
        bisect.insort(pts_list, x)
    return -1
    
print(solve(k_pts, m, pts_list))