Should I simply pick the last number in each list or should I pick the highest number in the list?

I am confused with the the first test case, where the sum ought to be 23. If I pick the last number in the list, the sum turns out to be 17 and not 23.

checkio([
[1],
[2, 3],
[3, 3, 1],
[3, 1, 5, 4],
[3, 1, 3, 1, 3],
[2, 2, 2, 2, 2, 2],
[5, 6, 4, 5, 6, 4, 3]
])

Created at: Dec. 23, 2013, 4:02 p.m.; Updated at: March 29, 2016, 6:08 a.m.