#include <bits/stdc++.h>
using namespace std;
const int inf = 1 << 28;
const double INF = 1e12, EPS = 1e-9;
void run() {
  int n, d[1000];
  cin >> n;
  for (int i = 0; i < n; i++) cin >> d[i];
  double l = -inf, u = inf;
  for (int i = 0; i < n; i++) {
    l = max(l, d[i] / (i + 1.0));
    u = min(u, (d[i] + 1) / (i + 1.0));
  }
  int a = (int)(l * (n + 1)), b = (int)(u * (n + 1) - EPS);
  if (a == b)
    printf("unique\n%d\n", a);
  else
    puts("not unique");
}
int main() { run(); }
