eval"N,M="+gets.split*?,
x=gets.to_i
a=(1...N).map{gets.to_i}.sort
p a.bsearch{|y|b=a.dup;b.delete_at b.index y;i=0;(N-3).downto(0).count{|j|i+=1while i<j&&x+y>=b[i]+b[j];i<j&&i+=1}<M}||-1