#include <bits/stdc++.h>
using namespace std;
static const double EPS = 1e-11;
int main() {
  istream &fin = cin;
  FILE *fpin = stdin;
  double maxa = 1e100, mina = 0;
  int n;
  fin >> n;
  n++;
  vector<int> gs(n);
  gs[0] = 0;
  for (int i = 1; i < n; i++) {
    fin >> gs[i];
  }
  for (int i = 1; i < n; i++) {
    mina = max(mina, gs[i] * 10. / i);
    maxa = min(maxa, ((gs[i] + 1) * 10. - EPS) / i);
  }
  long long d1 = (long long)floor(mina * n / 10.);
  long long d2 = (long long)floor(maxa * n / 10.);
  if (d1 != d2)
    cout << "not unique" << endl;
  else {
    cout << "unique" << endl;
    cout << d1 << endl;
  }
}
