import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;

public class No00000394_Main3 {
	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	public static void main(String[] args) throws IOException {
		String[] strArr = br.readLine().split(" ");
		int[] arr = new int[strArr.length];
		for(int i = 0; i < strArr.length; i++) {
			arr[i] = Integer.parseInt(strArr[i]);
		}
		Arrays.sort(arr);
		int score = 0;
		for(int i = 1; i <= 4; i++) {
			score += arr[i];
		}
		System.out.println(String.format("%.2f", score / 4.0));
	}
}