// 標準入力から 3 つの数値を入力し、平均を求めるプログラム

import java.io.*;
import java.lang.*;

public class AverageAnother {
  public static void main(String[] args) {
    int num1, num2, num3;
    double result;

    try {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      num1 = Integer.parseInt(br.readLine());
      num2 = Integer.parseInt(br.readLine());
      num3 = Integer.parseInt(br.readLine());

      result = (double) (num1 + num2 + num3) / 3;
      System.out.println(result);
    }
    catch (IOException ioe) {
    }
    catch (NumberFormatException nfe) {
      System.out.println("半角英数で数値を入力してください。");
    }
  }
}