import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.stream.Stream;

public class No00000394_Main {
	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	public static void main(String[] args) throws IOException {
		int[] arr = Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).sorted().toArray();
		int score = 0;
		for(int i = 1; i <= 4; i++) {
			score += arr[i];
		}
		System.out.println(String.format("%.2f", score / 4.0));
	}
}