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 |ai|
		b = a.dup
		b.delete_at(a.index ai)
		j = b.size - 1
		cnt =
			(0...b.size).count do |i|
				j -= 1 while i < j && x + ai >= b[i] + b[j]
				if i >= j
					false
				else
					j -= 1
					true
				end
			end
		cnt >= m
	end || n - 1
puts pos > 0 ? a[pos - 1] : -1