Find the n-th number made of even digits only
Given a number n, find out the n-th positive number made up of even digits (0, 2, 4, 6, 8) only. First few numbers made of even digits are 0, 2, 4, 6, 8, 20, 22, 24....... Examples : Input : 2 Output : 2 Second number made of 0, 2, 4, 6, 8 is 2 Input : 10 Output : 28 Naive Approach A naive approach