#include <bits/stdc++.h>
using namespace std;
bool asdfill[1100000];
int main() {
  int n;
  cin >> n;
  int last_known;
  for (int i = 0; i < (n); ++i) {
    int a;
    cin >> a;
    asdfill[a] = true;
    last_known = a;
  }
  double min_alpha = 10;
  double max_alpha = 1e200;
  int fills_done = 1;
  for (int p = 1;; ++p) {
    double alpha = (p * 10 + 10.0) / fills_done;
    if (p <= last_known) {
      if (asdfill[p]) {
        max_alpha = min(max_alpha, alpha);
        ++fills_done;
      } else {
        min_alpha = max(min_alpha, alpha);
      }
    } else {
      if (max_alpha <= alpha + 1e-8) {
        cout << "unique\n" << p;
        exit(0);
      } else if (min_alpha <= alpha - 1e-8) {
        cout << "not unique";
        exit(0);
      }
    }
  }
  return 0;
}
