P2902 [USACO08MAR] Pearl Pairing G

At Bessie's recent birthday party, she received $N(2 \le N \le 10^5,N\equiv0\pmod{2})$ pearls, each painted one of C different colors ($1\le C \le N$). Upon observing that the number of pearls $N$ is always even, her creative juices flowed and she decided to pair the pearls so that each pair of pearls has two different colors. Knowing that such a set of pairings is always possible for the supplied testcases, help Bessie perform such a pairing. If there are multiple ways of creating a pairing, any solution suffices.

Line $1$: Two space-separated integers: $N$ and $C$. Lines $2 \ldots C+1$: Line $i+1$ tells the count of pearls with color $i$: $C_i$.

Lines $1\ldots \dfrac{N}{2}$: Line $i$ contains two integers $a_i$ and $b_i$ indicating that Bessie can pair two pearls with respective colors $a_i$ and $b_i$.

There are $8$ pearls and $3$ different colors. Two pearls have color $\mathrm{I}$; two have color $\mathrm{II}$; four have color $\mathrm{III}$. Bessie pairs each pearl of color $\mathrm{III}$ with one of color $\mathrm{I}$ and $\mathrm{Ii}$.