#include <bits/stdc++.h>
const int MAXN = 0;
const int MAXM = 0;
const int INF = 2000000000;
const int MOD = 1000000007;
using namespace std;
double eps = 0.0001;
int n;
int a[1000007];
double amin = 10, amax = INF;
int main() {
  a[0] = 0;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
  }
  for (int i = 1; i <= n; i++) {
    for (int j = a[i - 1] + 1; j <= a[i] - 1; j++) {
      amin = max(amin, (double)10 * (double)(j + 1) / (double)i);
    }
    amax = min(amax, (double)10 * (double)(a[i] + 1) / (double)i);
  }
  double left_min = (n + 1) * amin - 10 * a[n];
  double left_max = (n + 1) * amax - 10 * a[n];
  int l = (left_min + eps) / 10;
  int r = (left_max - eps) / 10;
  if (l == r) {
    printf("unique\n");
    printf("%d\n", a[n] + l);
  } else {
    printf("not unique\n");
  }
  return 0;
}
