def ascan; gets.split.map(&:to_i); end

strs_t = gets.to_i.times.map{gets.chomp}

best = 'z'*250
400.times do
    ans = ''
    strs = strs_t.map{|l| l.chars}
    while !strs.empty?
        item, i = strs.each_with_index.min{|a,b| a[0][0] == b[0][0] ? rand(-1..1) : a[0][0] <=> b[0][0]}
        ans << strs[i].shift
        strs.delete_at(i) if strs[i].empty?
    end
    best = [ans,best].min
end

puts best