#include <bits/stdc++.h>
using namespace std;
const long double eps = 1e-7;
int n;
long double l = 10.;
long double r = 1e100;
vector<int> stations;
int main() {
  cin >> n;
  stations.resize(n);
  for (int i = 0; i < n; i++) cin >> stations[i];
  for (int i = 0; i < n; i++) {
    int k = stations[i];
    l = max(l, (long double)10.0 * k / (i + 1));
    r = min(r, (long double)10.0 * (k + 1) / (i + 1));
  }
  long double fuel = (n + 1) * l - 10.0 * (stations[n - 1]);
  int minst = int(fuel / 10.0);
  fuel = (n + 1) * (r - eps) - 10.0 * (stations[n - 1]);
  int maxst = int(fuel / 10.0);
  if (maxst > minst) {
    cout << "not unique";
    return 0;
  }
  cout << "unique\n";
  cout << stations[n - 1] + minst;
}
