#include <bits/stdc++.h>
using namespace std;
double l, r;
int n;
int main() {
  scanf("%d", &n);
  l = 0;
  r = 1000000000;
  for (int i = 0; i < n; i++) {
    int x, y;
    scanf("%d", &x);
    l = max(l, 1.0 * x / (i + 1));
    r = min(r, (1.0 * x + 1) / (i + 1));
  }
  l *= (n + 1);
  r *= (n + 1);
  l = int(l);
  r = int(r - 0.00000001);
  if (l == r) {
    printf("unique\n");
    printf("%d", int(l));
  } else
    printf("not unique");
}
