Find the sum 2

Very easy

Execution time limit is 1 second

Runtime memory usage limit is 128 megabytes

For the given value of $n$ find the sum

\frac{1}{s in 1} + \frac{1}{s in 1 + s in 2} + ... + \frac{1}{s in 1 + s in 2 + ... + s in n}

Input

One integer $n (n \leq 1000)$ .

Print the value of the sum with $6$ decimal digits.

Input #1

Answer #1

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