#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int ainfnum = 1, ainfdiv = 1, asupnum = 1000000000, asupdiv = 1;
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    int a;
    cin >> a;
    if (ainfnum * i < a * ainfdiv) {
      ainfnum = a;
      ainfdiv = i;
    }
    if (asupnum * i > (a + 1) * asupdiv) {
      asupnum = (a + 1);
      asupdiv = i;
    }
  }
  long long int posainf = (n + 1) * ainfnum / ainfdiv;
  long long int posasup =
      (n + 1) * asupnum / asupdiv - ((n + 1) * asupnum % asupdiv == 0);
  if (posainf >= posasup)
    cout << "unique" << endl << posasup << endl;
  else
    cout << "not unique" << endl;
}
