#include <bits/stdc++.h>
using namespace std;
int v[1005], n;
double cur, eps = 1e-7;
int check(double r) {
  int i, f, num;
  cur = r;
  f = 0;
  for (i = 1; i <= n; i++) {
    num = (int)(cur / 10 + eps);
    if (num < v[i] - v[i - 1]) {
      f = -1;
      break;
    }
    if (num > v[i] - v[i - 1]) {
      f = 1;
      break;
    }
    cur = cur - num * 10. + r;
  }
  return f;
}
int main() {
  int i, a, num, f, v1, v2;
  double p, q, r, p1, q1;
  cin >> n;
  for (i = 1; i <= n; i++) cin >> v[i];
  p1 = v[1];
  for (i = 2; i <= n; i++) {
    p1 = max(p1, v[i] / (i + 0.));
  }
  q1 = v[1] + 1;
  for (i = 2; i <= n; i++) {
    q1 = min(q1, (v[i] + 1) / (i + 0.));
  }
  v1 = (int)(p1 * (n + 1) + eps);
  v2 = (int)((q1 - eps) * (n + 1) + eps);
  if (v1 < v2)
    printf("not unique");
  else
    printf("unique\n%d", v1);
}
