#include <bits/stdc++.h>
using namespace std;
const int MAX = 1010;
const double EPS = 1e-8;
const double INF = 1e10;
int n;
int main() {
  cin >> n;
  double l = -INF, r = INF;
  for (int i = 0; i < n; i++) {
    double a;
    cin >> a;
    l = max(l, a / (i + 1));
    r = min(r, (a + 1) / (i + 1));
  }
  l *= (n + 1);
  r *= (n + 1);
  if ((int)l != (int)(r - EPS)) {
    puts("not unique");
  } else {
    puts("unique");
    cout << (int)l << endl;
  }
  return 0;
}
