#include <bits/stdc++.h>
using namespace std;
double L, R;
int n, i;
int a[10000];
double jami;
long long ans1, ans2, ans;
int main() {
  L = 10.0;
  R = 1000000000;
  cin >> n;
  for (i = 1; i <= n; i++) cin >> a[i];
  for (i = 1; i <= n; i++) {
    L = max(L, (double)((double)a[i] / i) * 10.0);
    R = min(R, (double)((double)(a[i] + 1) / i) * 10.0);
  }
  R -= 0.000000001;
  jami = (n + 1) * L;
  jami -= 10 * a[n];
  jami = floor(jami);
  ans1 = jami / 10;
  jami = (n + 1) * R;
  jami -= 10 * a[n];
  jami = floor(jami);
  ans2 = jami / 10;
  if (ans1 == ans2) {
    cout << "unique" << endl;
    cout << a[n] + ans1 << endl;
    return 0;
  }
  cout << "not unique" << endl;
}
