#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const int N = 1100;
int a[N];
int main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  for (int i = 0; i < (n); i++) cin >> a[i];
  double na = 1e18;
  double ma = 10;
  int cnt = 0;
  for (int i = 0; i < (n); i++) {
    cnt++;
    na = min(na, (10.0 + 10.0 * a[i]) / (double)cnt);
    ma = max(ma, (10.0 * a[i]) / (double)cnt);
  }
  cnt++;
  double now = (double)cnt * na - 10.0 * a[n - 1];
  long long ans1 = (long long)(now - 0.0001);
  now = (double)cnt * ma - 10.0 * a[n - 1];
  long long ans2 = (long long)(now + 0.0001);
  if (ans1 / 10 != ans2 / 10) {
    cout << "not unique"
         << "\n";
  } else {
    cout << "unique"
         << "\n";
    cout << a[n - 1] + ans1 / 10 << "\n";
  }
}
