#include <bits/stdc++.h>
using namespace std;
const int MaxN = (1000 * 1000) + 1000;
const long double Eps = 0.00000001;
int n, m;
long double Min = 10.0, Max = 1000000000000.0;
long double Counter = 0;
int Maxi = 0;
bool Mark[MaxN];
void Input() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> m;
    Mark[m] = true;
    Maxi = max(Maxi, m);
  }
}
void Run() {
  Counter = 0;
  for (int i = 1; i <= Maxi; i++) {
    if (!Mark[i]) {
      Min = max(Min,
                (10.0 * ((long double)(i + 1))) / ((long double)(Counter + 1)));
    } else {
      Max = min(Max,
                (10.0 * ((long double)(i + 1))) / ((long double)(Counter + 1)));
      Min = max(Min, (10.0 * ((long double)i)) / ((long double)(Counter + 1)));
      Counter++;
    }
  }
  Max -= Eps;
}
int main() {
  Input();
  Run();
  long double MaxRun, MinRun, a1, a2;
  Counter++;
  MinRun = (Counter * Min) - (long double)((long double)Maxi * 10.0);
  MaxRun = (Counter * Max) - (long double)((long double)Maxi * 10.0);
  a1 = MinRun / 10.0;
  a2 = MaxRun / 10.0;
  int mia = a1, mib = a2;
  if (mia != mib) {
    cout << "not unique" << endl;
  } else {
    cout << "unique" << endl;
    cout << Maxi + mia << endl;
  }
  return 0;
}
