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 <bits/stdc++.h>
int main() {
  int i, sum, x, s[1000];
  scanf("%d", &s[0]);
  sum = s[0];
  for (i = 1; i < 5; i++) {
    scanf("%d", &s[i]);
    sum += s[i];
  }
  if (sum == 0)
    printf("-1");
  else if (sum % 5 == 0) {
    x = sum / 5;
    printf("%d", x);
  } else
    printf("-1");
  return 0;
}
