#include <bits/stdc++.h>
using namespace std;
int a[10001];
double eps = 1e-8;
int main() {
  int n, i, j;
  while (scanf("%d", &n) > 0 && n) {
    double low = 10, high = 1e7;
    for ((i) = 0; (i) < (n); (i)++) scanf("%d", &a[i]);
    sort(a, a + n);
    for ((i) = 0; (i) < (n); (i)++) {
      high = min(high, 10 * (a[i] + 1) / (double)(i + 1));
      if (i < n - 1)
        for (j = a[i] + 1; j < a[i + 1]; j++)
          low = max(low, 10 * (j + 1) / (double)(i + 2));
    }
    int x = (int)(((n + 1) * low) / 10);
    int y = (int)(((n + 1) * high - eps) / 10);
    if (x == y)
      printf("unique\n%d\n", x);
    else
      printf("not unique\n");
  }
  return 0;
}
