#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int* A = new int[n];
  for (int i = 0; i < n; i++) cin >> A[i];
  double amin = 10 * A[0];
  double amax = 10 * (A[0] + 1);
  for (int i = 1; i < n; i++) {
    amin = max(amin, ((double)10 * A[i]) / ((double)(i + 1)));
    amax = min(amax, ((double)10 * (A[i] + 1)) / ((double)(i + 1)));
  }
  double nmin = amin * (double)(n + 1) / ((double)10);
  double nmax = amax * (double)(n + 1) / ((double)10);
  int a1 = (int)nmin;
  int a2 = (int)(nmax - 0.0000001);
  if (a1 == a2) {
    cout << "unique" << endl << a1;
    return 0;
  }
  cout << "not unique";
  return 0;
}
