#include <bits/stdc++.h>
using namespace std;
long long power(long long a, long long b) {
  if (b == 0) return 1;
  if (b % 2 == 0) return power(a, b / 2);
  return (a * power(a, b / 2));
}
bool is[1000001];
double bef[1000001];
const double eps = 0.00000001;
int main() {
  int n;
  cin >> n;
  int maxn = 0;
  for (int i = 0; i < n; i++) {
    int k;
    cin >> k;
    maxn = (k > maxn) ? k : maxn;
    is[k] = true;
  }
  int sum = 0;
  double mina = 10.0, maxa = 1000000000000.0;
  for (int i = 1; i <= maxn; i++) {
    bef[i] = sum;
    sum += is[i];
  }
  for (int i = 1; i <= maxn; i++) {
    if (is[i]) {
      maxa = (maxa < (double)(10.0 * (i + 1)) / (bef[i] + 1))
                 ? maxa
                 : (double)(10.0 * (i + 1)) / (bef[i] + 1);
      mina = (mina > (double)(10.0 * i) / (bef[i] + 1))
                 ? mina
                 : (double)(10.0 * i) / (bef[i] + 1);
    } else {
      mina = (mina > (double)(10.0 * (i + 1)) / (bef[i] + 1))
                 ? mina
                 : (double)(10.0 * (i + 1)) / (bef[i] + 1);
    }
  }
  maxa -= eps;
  double minrem = ((bef[maxn] + 2) * mina) - (maxn * 10.0);
  double maxrem = ((bef[maxn] + 2) * maxa) - (maxn * 10.0);
  double a1 = minrem / 10.0;
  double a2 = maxrem / 10.0;
  int mia = a1, maa = a2;
  if (mia != maa) {
    cout << "not unique\n";
  } else {
    cout << "unique\n";
    cout << mia + maxn << endl;
  }
  return 0;
}
