#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
int a[1010];
int main() {
  int i, n;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) scanf("%d", &a[i]);
  double mi, ma;
  mi = 10;
  ma = 1000000000;
  for (i = 1; i <= n; i++) {
    mi = max(mi, (double)a[i] * 10.0 / i);
    ma = min(ma, ((double)a[i] + 1.0) * 10.0 / i);
  }
  ma = ma * (n + 1) / 10.0;
  mi = mi * (n + 1) / 10.0 - 1.0;
  int beg, end;
  beg = int(mi + eps) + 1;
  end = int(ma - eps);
  if (beg == end)
    printf("unique\n%d\n", beg);
  else
    printf("not unique\n");
  return 0;
}
