Crying Colours

You have a total of $3N$ balls of colours $Red$, $Blue$ and $Green$. There are exactly $N$ balls of each colour. These $3N$ balls are now distributed to $3$ boxes such that each box contains exactly $N$ balls. You are given the contents of each box. You would like the $1^{st}$ box to contain all the **red** balls, the $2^{nd}$ box to contain all the **green** balls, and the $3^{rd}$ box to conta