How to generate n= 1000,000,000,000th even digit in c++ ? Time : 1 second

I'm novice to Programming . I can find even digit but my algorithm complexity O(n*n).Here n size is to much.So need efficient idea.Can anyone help me? For example, first some even digits consist number are 0 , 2 , 4 , 6 , 8 , 20 , 22 , 24 , 26 , 28 , 40 etc. Thanks in advance.