#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i, l, r;
  double x, mi = 0, ma = 1e12;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%lf", &x);
    mi = max(mi, x / i);
    ma = min(ma, (x + 1) / i);
  }
  l = (int)floor(mi * (n + 1) + 1e-9);
  r = (int)floor(ma * (n + 1) - 1e-9);
  if (l == r)
    printf("unique\n%d\n", l);
  else
    puts("not unique");
}
