Problem Description

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.

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