A magical string s consists of only '1' and '2' and obeys the following rules: The string s is magical because concatenating the number of contiguous occurrences of characters '1' and '2' generates the string s itself. The first few elements of s is s = "1221121221221121122...... ". If we group the consecutive 1's and 2's in s, it will be "1 22 11 2 1 22 1 22 11 2 11 22 ...... " and the occurrences of 1's or 2's in each group are "1 2 2 1 1 2 1 2 2 1 2 2 ...... ". You can see that the occurrence sequence is s itself. Given an integer n, return the number of 1's in the first n number in the magical string s.