#include <bits/stdc++.h>
using namespace std;
double eps = 1e-10;
int n;
double a[2000];
double mn, mx;
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  mn = 0, mx = 999999999.0;
  for (int i = 0; i < n; i++)
    mn = max(mn, a[i] / (double)(i + 1)),
    mx = min(mx, (a[i] + 1) / (double)(i + 1));
  if ((int)((double)(n + 1) * mn) == (int)((double)(n + 1) * mx - eps)) {
    cout << "unique\n";
    cout << (int)((double)(n + 1) * mn) << endl;
  } else
    cout << "not unique\n";
  {
    int _;
    cin >> _;
  }
}
