White Wall

Toofan loves white walls! He recently painted a wall with some colors: **Red (R)**, **Green (G)**, and **Blue (B)**. However, he realized that the wall doesn't look as bright and white as he imagined. Toofan's wall has length $N$, meaning it has $N$ positions placed in a line, and each position can be painted in one color — either red, blue, or green. You are given a string $S$ of length $N$, d