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 the passengers will:

• Take their own seat if it is still available, and
• Pick other seats randomly when they find their seat occupied

Return the probability that the nth person gets 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 <= 105