Time Limit : sec, Memory Limit : KB

# Standard Deviation

You have final scores of an examination for n students. Calculate standard deviation of the scores s1, s2 ... sn.

The variance α2 is defined by

α2 = (∑ni=1(si - m)2)/n

where m is an average of si. 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
s1 s2 ... sn


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.

• n ≤ 1000
• 0 ≤ si ≤ 100

## Sample Input

5
70 80 100 90 20
3
80 80 80
0


## Sample Output

27.85677655
0.00000000