The Melancholy of Problem Setter

Roughly speaking, this problem asks you to create the checker of [*the problem used in December CookOff*](https://www.codechef.com/problems/RGBCONST). You are given a tree with $N$ vertices and a string $C$ of length $N$, consisting of the characters `'R'`, `'G'` and `'B'`. For each integer $i\ (1\leq i\leq N)$, $C_i$ is the color of vertex $i$ — `'R'` is for Red, `'G'` is for Green and `'B'` is