A very famous DJ has been recently invited to play in the closing party of a Computer Science conference. Trying to impress the participants of the event, he decided to use a program in order to choose the songs he would play at this party. However, the result was a disaster, since the way the program chose the songs was quite weird and repetitive.
First of all, the DJ has selected N songs among the set of songs he had available. The program used by the DJ then labels each of the songs using one different character from 'A' to 'Z'. The ith song is labeled using the ith character of the sequence 'A'-'Z'. The program chooses the songs to be played in the party in the order that their labels appear in the following infinite sequence of characters: first come all the words with one character in lexicographical order; then all the words with two characters in lexicographical order; then all the words with three characters in lexicographical order; and so on. For N = 3, this sequence would be ABCAAABACBABBBCCACBCCAAAAABAACABAABBABC...
At the end of the party, some people asked the DJ if he remembered which the first song played was. Others would like to know which the 25th was, and so on. The DJ remembers nothing but the strange pattern of repetition of the songs, so he urges you to help him and write a program which answers such queries.