URI Online Judge | 2774
# Sensor Accuracy

**Timelimit: 1**

By Adriene Magalhães, INATEL Brazil

The teacher is teaching you about sensors. This is a very important element in many applications. To better understand the concepts of precision, the teacher asked to perform a practical assembly of the Thermo Ind v4.0 sensor in the new Automation laboratory.

As a good student you wrote down the formula for calculating the accuracy of a sensor:

**\(\sigma\;=\;\sqrt{\frac{\sum_1^{QT}\left(\;X_i-\overline X\;\right)^2}{QT-1}}\)**

Where **QT** is the number of times the test was performed, \(X\)** **the value measured in each test and **\(\overline X\)** the mean of the values.

To perform the test you have been doing **H** hours testing, and every **M** minutes you have checked the **X** value of the temperature delivered by the sensor.

Now that you have the measurements, and as you have the ability to program, make a program that delivers sensor accuracy.

There are several test cases, each case consisting of two lines. The first one contains two values **H** and **M**. The second consists of the floating point values **X _{i}** indicating the value of each sensor measurement.

It is guaranteed that there will be at least 5 and at most 10^{5} measures per case and that these values are in the interval [0, 255] with two decimal places.

For each test case, print a single line with a number indicating the sensor's accuracy. The calculated value must be displayed with 5 digits after the decimal point.

Input Sample | Output Sample |

1 10 2.99 2.94 3.02 2.91 3.05 3.11 2 16 5.00 5.00 5.00 5.00 5.00 5.00 5.00 |
0.07312 0.00000 |