#include <fstream>
#include <iostream>
#include <cmath>
using namespace std;
double std_dev( double a [], int x );
const int MAX= 100;

int main ()
{
    double next;
    int index = 0;
    double a[MAX];

    cout << "I will give you the std deviation of a group of numbers less than "<< MAX << endl;
    cin >> next;
    while ((cin>>next) && (index < MAX))
    {
        a[index] = next;
        index++;
        cin >> next;
    }
    std_dev ( a , index );
}
double std_dev( double a [], int x )
{
    double average, y;
    double sum = 0;
    int i;
    for( i = 0; i < x;i++ )
        {
        sum = sum + a[i];
        }
    average = sum / x;
    sum = 0;
    for( i = 0; i < x; i++ )
    {
        y =pow((a[i]-average),2);
        //cout << s<<" ";
        sum = sum + y;
    }
cout <<(sqrt (sum / x));

return 0;
}