#include <bits/stdc++.h>
using namespace std;
double mi, ma, eps = 1e-9, mir, mar;
int n, k, lk;
int main() {
  scanf("%d", &n);
  scanf("%d", &k);
  mi = 10;
  ma = (k + 1) * 10. - eps;
  mir = 2 * mi - k * 10;
  mar = 2 * ma - k * 10;
  for (int i = 1; i < n; ++i) {
    lk = k;
    scanf("%d", &k);
    int passed = k - lk;
    int before = i + 1;
    if (passed * 10 > mir) {
      double r = (passed * 10 - mir) / before;
      mi += r;
    }
    mir = (before + 1) * mi - 10 * k;
    if ((passed + 1) * 10 < mar) {
      double r = (mar - (passed + 1) * 10 + eps) / before;
      ma -= r;
    }
    mar = (before + 1) * ma - 10 * k;
  }
  int imir = int(mir / 10), imar = int(mar / 10);
  if (imir == imar) {
    puts("unique");
    printf("%d", imir + k);
  } else
    puts("not unique");
  return 0;
}
