99 100 100 100 100
 57 83 11 4 93
 99 99 99 99 99
 100 0 0 0 0
 0 1 2 3 4
 93 100 99 90 98
 87 38 19 33 100
 1 1 1 1 1
 0 0 0 0 1
 2 3 4 5 6
 1 2 1 2 3
 0 0 0 0 0
 100 100 100 100 100
 43 83 1 0 23
 43 83 1 100 23
 56 0 0 0 4
 99 98 98 99 100

-1
 -1
 99
 20
 2
 96
 -1
 1
 -1
 4
 -1
 -1
 100
 30
 50
 12
 -1


import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintStream;
import java.util.StringTokenizer;

/**
 *
 * @author baha
 */
public class ProblemA {

    static Scanner in;
    static Output out;

    public static void main(String[] args) throws Exception {
        boolean isFile = false;
        String filenameIn = null;
        if (isFile) {
            in = new Scanner(filenameIn);
        } else {
            in = new Scanner();
            out = new Output(System.out);
        }
        int sum = 0;
        for (int i = 0; i < 5; i++) {
            sum += in.nextInt();
        }
        if (sum % 5 == 0 && sum >= 5) {
            System.out.println(sum / 5);
        } else if (sum < 5) {
            System.out.println(-1);
        } else {
            System.out.println(-1);
        }
        System.out.println(0 % 5);
    }

    private static class Scanner {

        StringTokenizer st = null;
        BufferedReader in;

        public Scanner() {
            in = new BufferedReader(new InputStreamReader(System.in));
        }

        public Scanner(String fileName) throws FileNotFoundException {
            in = new BufferedReader(new FileReader(fileName));
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens()) {
                st = new StringTokenizer(in.readLine());
            }
            return st.nextToken();
        }

        public String nextLine() throws IOException {
            return in.readLine();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public long nextLong() throws IOException {
            return Long.parseLong(next());
        }
    }

    private static class Output extends PrintStream {

        public Output(OutputStream out) {
            super(out);
        }

        public Output(File file) throws FileNotFoundException {
            super(file);
        }
    }
}
