In this Google Code Jam 2021 Round 1C problem 1 the expected solution in my sense to the test case below is:

8/18, i.e.,

0.4444444444

but the actual output is:

0.555555556

Could someone please explain why the actual output is not same as what i expect.

Test Case:

input:

5 18

17 4 4 18 6

output:

0.555555556

PS: This is my solution, which is also incorrect.