import java.math.BigDecimal; import java.math.RoundingMode; import java.util.Scanner;

public class Main {

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String input = sc.nextLine();
    String[] nums = input.split(" ");
    BigDecimal a = new BigDecimal(nums[0]);
    BigDecimal b = new BigDecimal(nums[1]);
    BigDecimal c = new BigDecimal(nums[2]);
    BigDecimal sum = a.add(b).add(c);
    BigDecimal divided = new BigDecimal(3);
    BigDecimal average = sum.divide(divided, 3,RoundingMode.HALF_EVEN);
    System.out.println(average);
}

}