#931 The ratio of product to the sum

   Calculate the ratio of the product numbers of natural numbers to their sum.

Specifications

   Input

   In single line set to a positive N, not exceeding 2·109.

   Output

   The desired ratio, calculated with an accuracy of 3 znachuschih digits after the decimal point.

Time Limit: 1 seconds
Balls for the passed test: 2
Complexity: 15%

Example

Example input

36

Example output

2.000


Problem URL: http://www.e-olimp.com.ua/en/problems/931