n = gets.to_i
ss = n.times.map { gets.chomp + "|"}
l = ss.inject(0){|s,v| s + (v.size - 1) }

puts l.times.inject("") {|r,i|
    ss.sort!
    c = ss[0][0]
    ss[0] = ss[0].slice(1,1000)
    r + c
}