#include <bits/stdc++.h>
using namespace std;
int i, n, a, b, c = 1e9, e;
int main() {
  long i, n, a;
  double l = -1e9, r = 1e9;
  scanf("%ld", &n);
  for (i = 1; i <= n; i++) {
    scanf("%ld", &a);
    l = max(l, 1.0 * a / i);
    r = min(r, 1.0 * (a + 1) / i);
  }
  l *= n + 1;
  r *= n + 1;
  r -= 1e-8;
  l += 1e-16;
  if ((long)l == (long)r)
    printf("unique\n%ld\n", (long)l);
  else
    puts("not unique");
  return 0;
}
