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.Scanner;
public class InitialBet {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
int c1=sc.nextInt();
int c2=sc.nextInt();
int c3=sc.nextInt();
int c4=sc.nextInt();
int c5=sc.nextInt();
int sum=0;
int i=2;
int a=0;
int b=0;
sum=c1+c2+c3+c4+c5;
while(i<sum){
	a=sum/i;
	if (a*i==sum){
		b=a;
		
		
		break;
	}
	else 
		i++;
	
	
}
if (a==b)
	System.out.print(i);
else 
	System.out.print(-1);
		

	}

}
