#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  double Min = 0.0;
  double Max = 1000000.0;
  int prev = -5;
  for (int a = 1; a <= n; a++) {
    double p;
    cin >> p;
    Min = max(Min, (double)p * 10 / a);
    Max = min(Max, (double)(p + 1) * 10 / a);
  }
  Max -= 0.0000001;
  Min += 0.0000001;
  int r = ceil((double)(n + 1) * Min / 10);
  int s = ceil((double)(n + 1) * Max / 10);
  if (r == s && Min < Max)
    cout << "unique" << endl << r - 1 << endl;
  else
    cout << "not unique" << endl;
  return 0;
}
