#include <bits/stdc++.h>
using namespace std;
const double EPS = 0.00000000001;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  double amin = a[0] * 10, amax = (a[0] + 1) * 10;
  for (int i = 1; i < n; ++i) {
    if ((double)(10 * a[i]) / (i + 1) > amin) {
      amin = (double)(10 * a[i]) / (i + 1);
    }
    if ((double)(10 * (a[i] + 1)) / (i + 1) < amax) {
      amax = (double)(10 * (a[i] + 1)) / (i + 1);
    }
  }
  int next1, next2;
  next1 = a[n - 1] + floor(((n + 1) * amin - a[n - 1] * 10) / 10);
  next2 = a[n - 1] + floor(((n + 1) * (amax - EPS) - a[n - 1] * 10) / 10);
  if (next2 == next1) {
    cout << "unique" << endl << next1;
  } else {
    cout << "not unique" << endl;
  }
  return 0;
}
