#include <bits/stdc++.h>
using namespace std;
long long power(long long a, long long b) {
  long long ans = 1;
  while (b > 0) {
    if (b % 2 != 0) {
      ans = (ans * a) % 1000000007;
    }
    a = ((a % 1000000007) * (a % 1000000007)) % 1000000007;
    b >>= 1;
  }
  return ans;
}
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int t = 1;
  while (t--) {
    int n;
    cin >> n;
    int a[n];
    for (int i = 0; i < n; i++) cin >> a[i];
    double aa = 1, b = 0;
    double mi = 10, ma = 1e9;
    for (int i = 1; i <= a[n - 1]; i++) {
      double o = (10 * (i + 1)) / aa;
      if (binary_search(a, a + n, i)) {
        ma = min(ma, o);
        aa++;
      } else {
        mi = max(mi, o);
      }
    }
    double err = -0.0000001;
    ma += err;
    int val1, val2;
    val1 = ceil(((n + 1) * ma - 10 - err) / 10);
    val2 = ceil(((n + 1) * mi - 10 - err) / 10);
    if (val1 == val2) {
      cout << "unique" << '\n' << val1;
    } else
      cout << "not unique";
  }
  return 0;
}
