#include <stdio.h>

#define MAX_N (11234)

int notas[MAX_N];

int main(int argc, char *noargs[]) {
  int n, res, i, ave;
  for (;;) {
    if (scanf("%d", &n) == EOF) break;
    for (i = 0; i < n; ++i) {
      scanf("%d", &notas[i]);
    }
    ave = 0;
    for (i = 0; i < n; ++i) {
      ave += notas[i];
    }
    if (ave % n != 0) res = -1;
    else {
      ave /= n;
      res = 1;
      for (i = 0; i < n; ++i) {
	if (notas[i] < ave) res += ave - notas[i];
      }
    }
    printf("%d\n", res);
  }
  return 0;
}