5718번 - Abwords 스페셜 저지다국어

We call “word” every string, containing two or more capital letters A and B, starting with A. We define upon each word the following two actions, resulting in another word:

• R1: We keep all the letters untouched, except for the last one, which is changed: А becomes B and vice versa – B becomes A.
• R2: Let’s denote the starting word with w. We form a new word t out of w in the following way:
  • The first letter of t is A, of course.
  • Each next letter at position i (i > 1) t_i depends on the letters at positions i-1 and i in the original word w, namely: if w_i-1 = w_i, we make t_i = B; otherwise t_i = A.
  • We replace w by t.

The N-time consecutive applying of actions of type R1 and R2 in some order, starting with a given word w is called “N- transformation” of w if:

• After the application of these actions the resulting word tallies with the given one (w);
• All words received in between, in the transformation process, are different from one another and differ from the given word, too.

Consider a positive integer N, greater than 1. Write a program abwords, which finds out one word with as few letters as possible, which can be a start of an N-transformation, or ascertains that such word does not exist. 

One positive integer N > 1 is read from the standard input.

The program should write to the standard output:

• Line 1: one word with as few letters as possible, for which an N- transformation exists;
• Line 2: a string of N characters, each 1 or 2 with no delimiters. This should be the string of the rule numbers in the N-transformation. Applying all of them in the output order starting with the word in output line 1 should lead to its first reproduction without repeating words in the meantime.

Or

• One line with the message NO if such word does not exist. 

• 2 ≤ N ≤ 100 000

There is no word shorter than 4 letters that can start a sequence of 6 actions which reproduce it without repeating words in the meantime. On the other hand, for example, the word AABB with four letters has such sequence of actions (i.e., a 6-transformation for it exists):

AABB --2-> ABAB --2-> AAAA --1-> AAAB --2-> ABBA --1-> ABBA --2-> ABBB --2-> AABB