can anyone help me to find two node that are not adjacent to each other but has highest degree.

suppose node 1 with 4 degree, node 5 with 4 degree but node 1 and 5 are adjacent so we cant choose node 1 and 5. another node 8 has a degree of 3. and all other node has degree <= 3. also node 5 and 8 are not adjacent, so we can choose node 1 and 8, or 5 and 8. I did not come up with any idea so seeking for help