#include <bits/stdc++.h>
using namespace std;
int n;
int s[(1000 + 100)];
double maximum(double a, double b) { return ((a > b) ? a : b); }
double minimum(double a, double b) { return ((a < b) ? a : b); }
int next(double alpha) {
  double bak = alpha;
  int count = 0, last = 0;
  for (int i = 1; count <= n; i++) {
    bak -= 10;
    if (bak < 10) {
      bak += alpha, last = i, count++;
    }
  }
  return last;
}
int main() {
  cin >> n;
  double max, min;
  int t;
  cin >> t;
  s[0] = t;
  min = (t) / 1;
  max = (1 + t) / 1;
  for (int i = 2; i <= n; i++) {
    cin >> t;
    s[i - 1] = t;
    min = maximum(min, (t) / (double)i);
    max = minimum(max, (1 + t) / (double)i);
  }
  int p = (double)(n + 1) * min;
  int q = (double)(n + 1) * (max - 10e-10);
  if (p != q)
    cout << "not unique" << endl;
  else
    cout << "unique" << endl << p << endl;
  return 0;
}
