#include <bits/stdc++.h>
int a;
int main() {
  int n;
  long long p1, q1, p2, q2;
  scanf("%d", &n);
  float a_min = 10;
  double a_max = 1e9;
  p1 = 10;
  q1 = 1;
  for (int i = 0; i < n; i++) {
    scanf("%d", &a);
    if ((double)a * 10 / (i + 1) > a_min) {
      a_min = (double)a * 10 / (i + 1);
      p1 = a * 10;
      q1 = i + 1;
    }
    if ((double)(a * 10 + 10) / (i + 1) < a_max) {
      a_max = (double)(a * 10 + 10) / (i + 1);
      p2 = (a * 10 + 10);
      q2 = (i + 1);
    }
  }
  int a1 = p1 * (n + 1) / 10 / q1;
  int a2 = p2 * (n + 1) / 10 / q2;
  if (p2 * (n + 1) % (10 * q2) == 0) a2--;
  if (a1 == a2)
    printf("unique\n%d", a1);
  else
    printf("not unique");
}
