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 string S is the following: 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 above is the S itself. Given an integer N as input, return the number of '1's in the first N number in the magical string S. Note: N will not exceed 100,000. Example 1: Input: 6 Output: 3 Explanation: The first 6 elements of magical string S is "12211" and it contains three 1's, so return 3.