#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1);
const double eps = 1e-8;
int main() {
  int n, a[1200] = {0};
  scanf("%d", &n);
  double low = 0, high = 1e8;
  for (int i = 1; i < n + 1; ++i) {
    scanf("%d", &a[i]);
    low = max(low, 10.0 * a[i] / i);
    high = min(high, 10.0 * (a[i] + 1) / i);
  }
  int t1 = floor(((n + 1) * low + eps) / 10);
  int t2 = floor(((n + 1) * high - eps) / 10);
  if (t1 == t2) {
    cout << "unique" << endl;
    cout << t1 << endl;
  } else
    cout << "not unique" << endl;
  return 0;
}
