#include <bits/stdc++.h>
using namespace std;
double input[1000];
int main() {
  int nInput;
  cin >> nInput;
  for (int i = 0; i < nInput; i++) cin >> input[i];
  double a(0.0), b(10000000.0);
  for (int i = 0; i < nInput; i++) {
    a = max(a, input[i] / (double)(i + 1));
    b = min(b, (input[i] + 1.0) / (double)(i + 1));
  }
  a *= (double)(nInput + 1);
  b *= (double)(nInput + 1);
  int ia = a;
  if (ia + 1.0 < b)
    cout << "not unique" << endl;
  else
    cout << "unique\n" << ia << endl;
  return 0;
}
