import java.util.Scanner;

class Question394
{
	public static void main(String[] str)
	{
	
		Scanner scan = new Scanner(System.in);
		
		int score[] = new int[6];
		double point = 0;
		
		for(int i=0; i<6; i++){
			score[i] = scan.nextInt();
		}
		
		for(int i=1; i<5; i++){
			point += score[i];
		}
		
		System.out.printf("%.2f\n",point/4);
	}
}