import java.io.*;

class std{
		float value;
      LinkedList values;

	std(LinkedList list){
   	values = list;
   }

   public double value()throws DivideByZero{
   	double result;
      int count = 0;
      Integer next;
      double sumOfX = 0.0;
   	Iterator it = new Iterator(values);
      while((next = (Integer)it.getNext())!= null){
      	sumOfX = sumOfX + next.intValue();
         count = count + 1;
      }
      if (count > 0){
      	double average = sumOfX/count;
         Iterator it2 = new Iterator(values);
         sumOfX = 0.0;
         while((next = (Integer)it2.getNext())!= null){
      		sumOfX = sumOfX + (next.intValue()  - average)*(next.intValue()  - average);
      	}
         return sumOfX/(count-1);
      }else if (count ==1){
      			return 0;
      }else{
      	throw new DivideByZero();
      }

   }


}