Inefficient code in Codility test task - How to improve?

I did a sample on codility and finished the test task.

I only scored 8% on correctness and a 54% on performance.

However, the code I wrote gives the correct result. Here is my code, results and solution:

http://ift.tt/1OHLVT5

Can somebody explain why my code scored so low? And what to do to improve?

Mirza