#include <bits/stdc++.h>
using namespace std;
const int N = 1000;
int a[N];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < (int)n; i++) cin >> a[i];
  double mn = 0, mx = 1e9;
  for (int i = 0; i < (int)n; i++) {
    mn = max(mn, a[i] / (i + 1.0));
    mx = min(mx, (a[i] + 1.0 - 1e-9) / (i + 1.0));
  }
  int b = (int)(mn * (n + 1));
  int c = (int)(mx * (n + 1));
  if (b == c)
    printf("unique\n%d\n", b);
  else
    printf("not unique\n");
  return 0;
}
