Problem B
Simply Syntax
In the land of Hedonia the official language
is Hedonian. A Hedonian professor had noticed that many of her students still
did not master the syntax of Hedonian well. Tired of correcting the many
syntactical mistakes, she decided to challenge the students and asked them to
write a program that could check the syntactical correctness of any sentence
they wrote. Similar to the nature of Hedonians, the syntax of Hedonian is also
pleasantly simple. Here are the rules:
0. The only characters in the
language are the characters p through z and N, C, D, E, and I.
1. Every
character from p through z is a correct sentence.
2. If s is a
correct sentence, then so is Ns.
3. If s and t are
correct sentences, then so are Cst, Dst, Est, and
Ist.
4. Rules 0. to 3. are the only rules to determine the
syntactical correctness of a sentence.
You are asked to write a program
that checks if sentences satisfy the syntax rules given in Rule 0. - Rule 4.
Input:
The input consists of a number of sentences consisting only of
characters p through z and N, C, D, E, and I. Each sentence is ended by a
new-line character. The collection of sentences is terminated by the end-of-file
character. If necessary, you may assume that each sentence has at most 256
characters and at least 1 character.
Output:
The output consists of the answers YES for each well-formed
sentence and NO for each not-well-formed sentence. The answers are given in the
same order as the sentences. Each answer is followed by a new-line character,
and the list of answers is followed by an end-of-file character.
Sample Input:
Cp
Isz
NIsz
Cqpq
Sample Output:
NO
YES
YES
NO