#include <bits/stdc++.h>
using namespace std;
int n, a;
double minx, maxx;
int main() {
  cin >> n >> a;
  minx = a;
  maxx = a + 1;
  for (int i = 2; i <= n; i++) {
    cin >> a;
    minx = max(minx, a * 1.0 / i);
    maxx = min(maxx, (a + 1) * 1.0 / i);
  }
  minx *= n + 1, maxx *= n + 1;
  int minn = floor(minx);
  int maxn = floor(maxx);
  if (maxx == floor(maxx)) maxn--;
  if (minn != maxn) {
    cout << "not unique";
    return 0;
  }
  cout << "unique" << endl;
  cout << minn;
  return 0;
}
