#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/stack:16000000")
#pragma warning(disable : 4996)
const int inf = 1 << 25;
const double eps = 1e-9;
int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = (0); i < (n); ++i) cin >> a[i];
  double lb = 10;
  double ub = inf;
  for (int i = (0); i < (n); ++i) {
    lb = max(lb, a[i] * 10. / (i + 1));
    if (i) {
      ub = min(ub, a[i] * 10. / i);
    }
    ub = min(ub, (a[i] + 1) * 10. / (i + 1));
  }
  double mx = (n + 1) * (ub) / 10.;
  double mn = (n + 1) * lb / 10.;
  vector<int> ans;
  for (int i = floor(mn); ans.size() < 2 && i < mx - eps; ++i) ans.push_back(i);
  if (ans.size() > 1)
    puts("not unique");
  else {
    printf("unique %d\n", ans[0]);
  }
  return 0;
}
