#include <bits/stdc++.h>
const int MAXN = 51;
const int MAXM = 1;
const int MAXL = 1;
using namespace std;
int n, a[1001];
double l = -2000000000, r = 2000000000;
int main() {
  scanf("%d", &n);
  for (int i = 0, _n = (n); i < _n; i++) {
    scanf("%d", &a[i]);
  }
  for (int i = 0, _n = (n); i < _n; i++) {
    l = max(l, double(a[i] * 10) / (i + 1));
    r = min(r, double((a[i] + 1) * 10) / (i + 1));
  }
  int a, b;
  r -= 1e-6;
  l += 1e-6;
  a = floor(((n + 1) * l) / 10);
  b = floor(((n + 1) * r) / 10);
  if (a != b)
    printf("not unique\n");
  else
    printf("unique\n%d\n", a);
  return 0;
}
