#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  double a;
  cin >> n;
  double minn = 1, maxx = 1000000000000000.0;
  for (int i = 1; i <= n; i++) {
    cin >> a;
    double newmin, newmax;
    newmin = (a) / (i * 1.0);
    minn = max(minn, newmin);
    a += 1;
    newmax = (a) / (i * 1.0);
    maxx = min(maxx, newmax);
  }
  maxx *= n + 1;
  minn *= n + 1;
  minn += 0.0000001;
  maxx -= 0.0000001;
  if ((int)minn == int(maxx))
    cout << "unique" << endl << int(minn) << endl;
  else
    cout << "not unique" << endl;
  return 0;
}
