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

#include<stdio.h>
#include<conio.h>


int main()
{
	int i,sum=0,a;
	for(i=0;i<5;i++)
	{
		scanf("%d", &a);
		sum=sum+a;
	}
	if(sum%5==0)
		printf("%d", sum/5);
	else
		printf("-1");

	//getch();
	return 0;
}