#include <bits/stdc++.h>
using namespace std;
int a[1111], n;
int main() {
  pair<int, int> res = make_pair(INT_MIN, INT_MAX);
  cin >> n;
  for (int i = 0; i < (n); ++i) cin >> a[i];
  for (int i = 0; i < ((n + 1) / 2); ++i) {
    int l = a[i] + a[n - 1 - i];
    res.first = (res.first < (l)) ? (l) : res.first;
    res.second = (res.second > (l + 2)) ? (l + 2) : res.second;
  }
  if (res.second - res.first <= 1) {
    cout << "unique" << endl;
    cout << res.first << endl;
  } else
    cout << "not unique" << endl;
  return 0;
}
