#include <bits/stdc++.h>
using namespace std;
int mass[10000];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", mass + i);
  double minA = 0, maxA = 1e9;
  for (int i = 0; i < n; i++) {
    minA = max(minA, (double)mass[i] / (i + 1));
    maxA = min(maxA, (double)(mass[i] + 1) / (i + 1));
  }
  if ((int)(minA * (n + 1) + 0.0000001) == (int)(maxA * (n + 1) - 0.0000001))
    printf("unique\n%d", (int)(minA * (n + 1) + 0.0000001));
  else
    printf("not unique");
}
