import java.io.PrintStream;
import java.util.Scanner;

public class VarDiffExtended {
  public static void main(String[] args) {
    //    Initialization and Declaration
    Scanner sc = new Scanner(System.in);
    PrintStream ps = System.out;
    int[] a = new int[499]; // array a with maximum 499 number of elements
    int[] b = new int[250]; // array b with maximum 250 number of odd or even elements from array a
    int size_of_a = 0; // number of inserted elements - X
    int size_of_b = 0; // number of sample elements - Y
    int j = 0; // index of b array

    //    Inserting the values to an array
    for (int i = 0; sc.hasNextInt(); size_of_a++, i++)
      a[i] = sc.nextInt();
    ps.printf("%d elements are added.%n", size_of_a);

    if (a[0] % 2 != 0) {
      ps.printf("First element of an array is odd.%n");
      for(int i = 0 ; i < size_of_a; i++) {
        if(i % 2 != 0) {
          b[j++] = a[i];
          size_of_b ++;
        }
      }
    } else if (a[0] % 2 == 0) {
      ps.printf("First element of an array is even.%n");
      for(int i = 0 ; i < size_of_a; i++) {
        if(i % 2 == 0) {
          b[j++] = a[i];
          size_of_b ++;
        }
      }
    }
    ps.printf("Size of b is %d%n", size_of_b);

    //    Calculating total of sample
    double total_of_sample = 0;
    for (int i = 0; i < b.length; i++)
      total_of_sample += b[i];
    ps.printf("Total of sample is %.3f%n", total_of_sample);

    //      Calculating mean of sample
    double mean_of_sample = 0;
    mean_of_sample = total_of_sample / size_of_b;
    ps.printf("Mean of sample is %.3f%n", mean_of_sample);

    //    Calculating sample variance
    double sample_variance = 0;
    double sample_variance_before_division = 0;
    for (int i = 0; i < size_of_b; i++)
      sample_variance_before_division += (b[i] - mean_of_sample) * (b[i] - mean_of_sample);
    sample_variance = sample_variance_before_division / (size_of_b - 1);
    ps.printf("Sample variance is %.3f%n", sample_variance);

    //      Calculating total of population
    double total_of_population = 0;
    for (int i = 0; i < a.length; i++)
      total_of_population += a[i];
    ps.printf("Total of population is %.3f%n", total_of_population);

    //    Calculating mean of population
    double mean_of_population = 0;
    mean_of_population = total_of_population / size_of_a;
    ps.printf("Mean of population is %.3f%n", mean_of_population);

    //      Calculating population variance
    double population_variance = 0;
    double population_variance_before_division = 0;
    for (int i = 0; i < size_of_a; i++)
      population_variance_before_division += (a[i] - mean_of_population) * (a[i] - mean_of_population);
      // Note, we do not need to subtract one from the size of a
    population_variance = population_variance_before_division / (size_of_a);
    ps.printf("Population variance is %.3f%n", population_variance);

    //      Calculating the difference between sample variance and population variance
    double diff = population_variance - sample_variance;
    ps.printf("Difference of variances is %.3f%n", diff);

    //    Printing the difference with 3 digit numbers
    ps.printf("%.3f%n", Math.abs(diff));
    sc.close();
  }
}