#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:128000000")
double eps = 1e-8;
int main() {
  double r = 1e200;
  double l = -r;
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    int num;
    cin >> num;
    l = max(l, num / (i + 1.0) + eps);
    r = min(r, (num + 1 - eps) / (i + 1.0) - eps);
  }
  l = l * (n + 1);
  r = r * (n + 1);
  if ((long long)l == (long long)r) {
    cout << "unique" << endl;
    cout << (long long)l << endl;
  } else
    cout << "not unique" << endl;
  return 0;
}
