n passengers board an airplane with exactly n seats. The first passenger has lost the ticket and picks a seat randomly. But after that, the rest of passengers will: Take their own seat if it is still available, Pick other seats randomly when they find their seat occupied What is the probability that the n-th person can get his own seat? Example 1: Input: n = 1 Output: 1.00000 Explanation: The first person can only get the first seat. Example 2: Input: n = 2 Output: 0.50000 Explanation: The second person has a probability of 0.5 to get the second seat (when first person gets the first seat). Constraints: 1 <= n <= 10^5