#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, i, j, k;
  long double lo[5], mi;
  cin >> n;
  long long int p[n];
  cin >> p[0];
  lo[0] = p[0] + 0.0;
  lo[1] = p[0] + 1.0;
  for (i = 1; i < n; i++) {
    cin >> p[i];
    if (int(lo[0] * (i + 1)) != p[i]) {
      lo[0] = p[i] / (i + 1.0);
    }
    if (int(lo[1] * (i + 1)) != p[i]) {
      lo[1] = (p[i] + 1) / (i + 1.0);
    }
  }
  mi = lo[1] * (n + 1.0);
  if (mi - int(mi) == 0) mi--;
  if (int(lo[0] * (n + 1)) == int(mi)) {
    cout << "unique" << endl << int(lo[0] * (n + 1.0)) << endl;
  } else {
    cout << "not unique" << endl;
  }
  return 0;
}
