#include <bits/stdc++.h>
using namespace std;
int n, m, ta, tb;
double lt = 10, rt = 11111111;
int main() {
  scanf("%d", &n);
  for (auto i = 1; i <= n; i++)
    scanf("%d", &m), rt = min(rt, (m + 1) * 10.0 / i),
                     lt = max(lt, m * 10.0 / i);
  ta = floor(lt * (n + 1) / 10);
  tb = floor(rt * (n + 1) / 10) == rt * (n + 1) / 10 ? rt * (n + 1) / 10 - 1
                                                     : floor(rt * (n + 1) / 10);
  if (ta == tb)
    printf("unique\n%d\n", ta);
  else
    printf("not unique\n");
  return 0;
}
