#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  double lo = 0.0, hi = 10000000.0;
  for (int i = 1; i <= n; i++) {
    int sta;
    cin >> sta;
    lo = max(lo, (double)10.0 * sta / i);
    hi = min(hi, (double)10.0 * (sta + 1) / i);
  }
  int nextlo = floor(lo * (n + 1) / 10.0);
  int nexthi = ceil(hi * (n + 1) / 10.0);
  if (nextlo + 1 >= nexthi) {
    cout << "unique" << endl << nextlo << endl;
  } else {
    cout << "not unique" << endl;
  }
  return 0;
}
