import java.util.*;
 
class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner scan = new Scanner(System.in);
		double total=0, sum=0;
		
		while (scan.hasNext()){
			if (!scan.hasNextDouble()){
				scan.next();
				total += scan.nextDouble();
				sum++;
			}
			else	scan.next();
		}
		System.out.print(total/sum);
	}
}