#include <bits/stdc++.h>
#pragma comment(linker, "/stack:67108864")
using namespace std;
const long double EPS = 1e-9;
const long double PI = 3.1415926535897932384626433832795;
const int INF = 1000 * 1000 * 1000;
int main() {
  int n;
  cin >> n;
  vector<long double> a(n + 1);
  long double vmin = 0, vmax = INF;
  a[0] = 0;
  for (int i = 1; i <= int(n); ++i) {
    cin >> a[i];
    vmin = max(vmin, 10 * (a[i]) / i);
    vmax = min(vmax, 10 * (a[i] + 1) / i);
  }
  pair<int, int> ans;
  for (int b = int(a.back() + 1); b <= int(4 * a.back()); ++b) {
    long double jmin = 10.0 * b / (n + 1);
    long double jmax = 10.0 * (b + 1) / (n + 1);
    if (jmin < vmax && jmax > vmin) {
      ans.first++;
      ans.second = b;
    }
  }
  if (ans.first == 0) return 0;
  if (ans.first > 1)
    cout << "not unique" << endl;
  else {
    cout << "unique" << endl << ans.second << endl;
  }
  return 0;
}
