1. Shake your phone/device so the leaves at the bottom disappear.
Press each skull to turn them.
2. Solve the puzzles.
The top: 1 2 3 5 X is the Fibonacci Sequence.
This will give you the missing number = 8
Press the top left skull: 8 times
Press the bottom left skull: 9 times
Press the bottom right skull: 3 times