n, m = gets.split.map &:to_i
x = gets.to_i
a = Array.new(n - 1) { gets.to_i }.sort.reverse
pos =
	a.bsearch_index do |i|
		b = a.dup
		b.delete_at(b.index i)
		m <= b.each_slice(2).count { |j| x + i < j.sum }
	end
puts pos > 0 ? a[pos - 1] : -1