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.util.*;
import java.io.*;
public class Solution {
	public static void main(String[] args) {
    Scanner in=new Scanner(System.in);
    int[] as=new int[5];
    int sum=0;
    for(int i=0;i<5;i++){
    as[i]=in.nextInt();	
    sum=sum+as[i];
    }
    
	int t=0;
	if(sum%5!=0)
		System.out.println("-1");
		else
		{sum=sum/5;
		for(int i=0;i<5;i++){
			if(as[i]>0)
				t=t+as[i]-sum;
		}	
		System.out.println(t);
	}
}}


