#include <bits/stdc++.h>
using namespace std;
const int maxn = 1000 + 10, INF = 1e9;
double arr[maxn];
int main() {
  int n;
  double mina = 0, maxa = INF;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> arr[i];
  for (int i = 0; i < n; i++) {
    mina = max(mina, arr[i] * 10 / (i + 1));
    maxa = min(maxa, (arr[i] + 1) * (10) / (i + 1));
  }
  int k1, k2;
  k1 = (mina) * (n + 1) / 10;
  k2 = ceil((maxa) * (n + 1) - 1) / 10;
  if (k1 != k2)
    cout << "not unique" << endl;
  else {
    cout << "unique" << endl;
    cout << k1 << endl;
  }
  return 0;
}
