#include <bits/stdc++.h>
using namespace std;
double mn = 1e20, mx, t;
int n, low, high;
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> t;
    mn = min(mn, (t + 1 - 1e-8) / i);
    mx = max(mx, t / i);
  }
  n++;
  low = (int)(n * mx + 1e-9), high = (int)(n * mn + 1 - 1e-9);
  if (low + 1 == high)
    cout << "unique\n" << low;
  else
    cout << "not unique";
}
