#include <bits/stdc++.h>
int n, t, l, r;
double min, max;
int main() {
  scanf("%d%d", &n, &t);
  min = t;
  max = t + 1;
  for (int i = 2; i <= n; i++) {
    scanf("%d", &t);
    min = std::max(1.0 * t / i, min);
    max = std::min(1.0 * (t + 1) / i, max);
  }
  l = (int)floor(min * (n + 1));
  r = (int)floor(max * (n + 1)) -
      (int)((max * (n + 1)) == floor(max * (n + 1)));
  l != r ? printf("not unique") : printf("unique\n%d", l);
}
