Tanya and Password

给出长度为 $n+2$ 的字符串 $s$ 的全部 $n$ 个「长度为 $3$ 的子串」，求原串。若有解则输出 `YES` 与任意一个合法解，反之输出 `NO`。 字符集为大小写字母与数字，$1\le n\le2\times10^5$。

While dad was at work, a little girl Tanya decided to play with dad's password to his secret database. Dad's password is a string consisting of $ n+2 $ characters. She has written all the possible $ n $ three-letter continuous substrings of the password on pieces of paper, one for each piece of paper, and threw the password out. Each three-letter substring was written the number of times it occurred in the password. Thus, Tanya ended up with $ n $ pieces of paper. Then Tanya realized that dad will be upset to learn about her game and decided to restore the password or at least any string corresponding to the final set of three-letter strings. You have to help her in this difficult task. We know that dad's password consisted of lowercase and uppercase letters of the Latin alphabet and digits. Uppercase and lowercase letters of the Latin alphabet are considered distinct.

The first line contains integer $ n $ ( $ 1<=n<=2·10^{5} $ ), the number of three-letter substrings Tanya got. Next $ n $ lines contain three letters each, forming the substring of dad's password. Each character in the input is a lowercase or uppercase Latin letter or a digit.

If Tanya made a mistake somewhere during the game and the strings that correspond to the given set of substrings don't exist, print "NO". If it is possible to restore the string that corresponds to given set of substrings, print "YES", and then print any suitable password option.

5
aca
aba
aba
cab
bac

YES
abacaba

4
abc
bCb
cb1
b13

NO

7
aaa
aaa
aaa
aaa
aaa
aaa
aaa

YES
aaaaaaaaa