write a go solution for Description:
Monocarp has a dictionary of n words, consisting of 12 first letters of the Latin alphabet. The words are numbered from 1 to n. In every pair of adjacent characters in each word, the characters are different. For every word i, Monocarp also has an integer c_i denoting how often he uses this word.

Monocarp wants to design a keyboard that would allow him to type some of the words easily. A keyboard can be denoted as a sequence of 12 first letters of the Latin alphabet, where each letter from a to l appears exactly once.

A word can be typed with the keyboard easily if, for every pair of adjacent characters in the word, these characters are adjacent in the keyboard as well. The optimality of the keyboard is the sum of c_i over all words i that can be typed easily with it.

Help Monocarp to design a keyboard with the maximum possible optimality.

Input Format:
The first line contains one integer n (1<=n<=1000) — the number of words.

Then, n lines follow. The i-th of them contains an integer c_i (1<=c_i<=10^5) and a string s_i (2<=|s_i|<=2000) denoting the i-th word. Each character of s_i is one of 12 first letters of Latin alphabet, in lowercase. For every jin[1,|s_i|-1], the j-th character of s_i is different from the (j+1)-th one.

Additional constraint on the input: sumlimits_i=1^n|s_i|<=2000.

Output Format:
Print a sequence of 12 first letters of the Latin alphabet, where each letter from a to l appears exactly once, denoting the optimal keyboard. If there are multiple answers, you may print any of them.

Note:
None. Output only the code with no comments, explanation, or additional text.