"Solved" problem with trivial if-else solution for all cases. The problem doesn't stated correctly. OR test cases error.

P.S. Where is dislike button>

The problem and test cases are consistent.
At time zero they order one beer. After 30 minutes they order one more beer. So, within half an hour they've ordered two beers.
After another 30 minutes they order the sum of the previous two orders, which is two beers (1+1=2). So, within two half-hours they've ordered four beers. After yet another 30 minutes they again order the sum of the previous two orders, which is now three beers (1+2=3). So, within three half-hours they've ordered seven beers. And they continue on, thenceforth always ordering the sum of the preceding two orders. For example, the following order would be five beers (2+3=5), so the cumulative total after four half-hours would be twelve beers.
This is a very famous sequence, albeit in a different context.
(It would have been better to have more text cases, though.)

Good problem, but you could add more test cases, like n = 0, which should be 1. And a higher n, 144, which should be much greater than 2 billion beers (after 3 days straight at Octoberfest, wow). Unfortunately, It is impossible to calculate the beer for all 16 to 18 days within machine precision.