# Standard Deviation

You have final scores of an examination for `n` students. Calculate standard deviation of the scores `s`_{1}, `s`_{2} ... `s`_{n}.

The variance α^{2} is defined by

α^{2} = (∑^{n}_{i=1}(s_{i} - m)^{2})/n

where `m` is an average of `s`_{i}.
The standard deviation of the scores is the square root of their variance.

## Input

The input consists of multiple datasets. Each dataset is given in the following format:

`n`
`s`_{1} `s`_{2} ... `s`_{n}

The input ends with single zero for `n`.

## Output

For each dataset, print the standard deviation in a line. The output should not contain an absolute error greater than 10^{-4}.

## Constraints

## Sample Input

5
70 80 100 90 20
3
80 80 80
0

## Sample Output

27.85677655
0.00000000