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 s = 0, ar[5], t = 0;
  for (int i = 0; i < 5; ++i) {
    scanf("%d", &ar[i]);
    s += ar[i];
  }
  if (s % 5 || s == 0)
    printf("-1\n");
  else {
    for (int i = 0; i < 5; ++i)
      if (ar[i] % 2) ++t;
    if ((((s / 5) % 2) && (t == 1 || t == 3 || t == 5)) ||
        (!((s / 5) % 2) && (t == 0 || t == 2 || t == 4)))
      printf("%d\n", s / 5);
    else
      printf("-1\n");
  }
  return 0;
}
