import java.text.DecimalFormat;
import java.util.Scanner;
public class Testpoj1004 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
float value = 0 ;
for(int i = 0 ; i < 12 ; ++i ){
value += Float.valueOf(scanner.nextLine()).floatValue();
}
value = value / 12;
DecimalFormat df = new DecimalFormat(".00");
String str = df.format(value);
System.out.println("$" +str);
}
}