Let's mark Ak the volume of Santo's
k-th bottle in the row and Sk
the maximal volume of alcohol Santo can drink while
drinking only from first k bottles. Obviously:
S1 = A1,
S2 = A1 + A2 and
S3 = max{A1 + A2,
A1 + A3, A2 + A3}.
Now, for some k (4 ≤= k ≤= N) let's assume that
we know all the numbers S1, S2, ...
Sk-1. From the problem description is easy
to figure out that
Sk = max{Sk-1,
Sk-2 + Ak,
Sk-3 + Ak-1 + Ak}.
What is an easy recurent formula, which can be computed straightforward in one loop.