#include <bits/stdc++.h>
int i, n, a, b, c = 1e9, e;
int main() {
  std::cin >> n;
  for (; i < n; i++) {
    std::cin >> a;
    e = a * (n + 1) / (i + 1.0);
    if (b < e) b = e;
    e = (a + 1.0 - 1e-9) * (n + 1) / (i + 1.0);
    if (c > e) c = e;
  }
  if (b == c)
    std::cout << "unique\n" << b;
  else
    std::cout << "not unique\n";
}
