#include <bits/stdc++.h>
using namespace std;
int main() {
  int i;
  double n, a[1005];
  scanf("%lf", &n);
  for (i = 1; i <= (int)n; i++) scanf("%lf", &a[i]);
  double _min = 10000005, _max = -1;
  for (i = 1; i <= (int)n; i++) {
    if (_min > (double)(10.0 * a[i] + 10.0) / (double)(i))
      _min = (double)(10.0 * a[i] + 10.0) / (double)(i);
    if (_max < (double)(10.0 * a[i]) / (double)(i))
      _max = (double)(10.0 * a[i]) / (double)(i);
  }
  if (_min * (n + 1) / 10.0 <= (int)(_max * (n + 1) / 10 + 1))
    printf("unique\n%d\n", (int)(_max * (n + 1) / 10));
  else
    printf("not unique\n");
  return 0;
}
