#include <bits/stdc++.h>
using namespace std;
int main() {
  size_t n = 0;
  cin >> n;
  double l = -1e10, r = 1e10;
  vector<size_t> stations;
  for (size_t i = 0; i < n; ++i) {
    size_t a;
    cin >> a;
    stations.push_back(a);
    l = max(l, (double)stations[i] / (i + 1));
    r = min(r, ((double)stations[i] + 1.0) / (i + 1));
  }
  l *= n + 1;
  r *= n + 1;
  if ((int)l != (int)(r - 1e-8)) {
    cout << "not unique";
  } else {
    cout << "unique" << endl;
    cout << (int)l << endl;
  }
  return 0;
}
