#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, x;
  scanf("%d", &n);
  double left = 10, right = 100000000;
  for (int i = 1; i <= n; i++) {
    scanf("%d", &x);
    left = max(left, 10.0 * x / i);
    right = min(right, 10.0 * (x + 1) / i);
  }
  int a = (int)(left * (n + 1) / 10);
  int b = (int)((right - 1e-12) * (n + 1) / 10);
  if (a != b)
    puts("not unique");
  else {
    puts("unique");
    printf("%d\n", a);
  }
  return 0;
}
