#216155. [ICPC 2023 NAC] First Last

Alice and Bob are playing a word game. They start with a list of words, and they alternate turns. Alice goes first; she chooses a starting word from the list. On each subsequent turn, the current player must choose a word from the list that starts with the same letter that ends the word chosen by the other player in the previous turn. No word can be used more than once. At some point one of them will not be able to choose a word; that player loses.

Assume Alice and Bob both play optimally. How many words from the list, when chosen as the first word by Alice, lead to a win for her?

The first line of input contains a single integer () which is the number of words.

Each of the next lines contains a single word consisting only of the lower-case letters ‘a’ through ‘z’. Each word will be from two to fifteen letters long. All words will be distinct. There will be at most three distinct letters at the beginning and end of all words. Alice and Bob may only choose words from this list.

Output a single integer, which is the number of words from the list which force a win for Alice if she chooses it first, and both Alice and Bob play optimally.

样例输入 1

3
attic
climb
alpha

样例输出 1

2

样例输入 2

22
agora
alpha
antic
aorta
apnea
arena
aroma
attic
basic
blurb
china
circa
civic
climb
cobra
cocoa
comic
comma
conic
crumb
cubic
cynic

样例输出 2

6