#include <bits/stdc++.h>
using namespace std;
const long long N = 2007;
long long n;
long long a[N];
bool small(double x) {
  for (long long i = 1; i <= n; ++i) {
    if ((long long)(x * i) == a[i]) continue;
    if ((long long)(x * i) < a[i]) return 1;
    if ((long long)(x * i) > a[i]) return 0;
  }
  return 0;
}
bool big(double x) {
  for (long long i = 1; i <= n; ++i) {
    if ((long long)(x * i) == a[i]) continue;
    if ((long long)(x * i) < a[i]) return 0;
    if ((long long)(x * i) > a[i]) return 1;
  }
  return 0;
}
long long get(double x) { return (long long)(x * (n + 1)); }
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (long long i = 1; i <= n; ++i) cin >> a[i];
  const double EPS = 1e-8;
  double l = 0, r = 1e9;
  for (long long t = 0; t < 100; ++t) {
    double m = (l + r) / 2;
    if (small(m))
      l = m;
    else
      r = m;
  }
  auto res_l = r + EPS;
  l = 0, r = 1e9;
  for (long long t = 0; t < 100; ++t) {
    double m = (l + r) / 2;
    if (big(m))
      r = m;
    else
      l = m;
  }
  auto res_r = l - EPS;
  if (get(res_l) == get(res_r)) {
    cout << "unique\n";
    cout << get(res_l) << '\n';
  } else {
    cout << "not unique\n";
  }
}
