#include <bits/stdc++.h>
using namespace std;
int a[1005];
double L = 10, R = 1e9;
int main(void) {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++) {
    L = max(10. * a[i] / i, L);
    R = min((10. * a[i] + 10. - 1e-9) / i, R);
  }
  int tL = (int)floor(((n + 1) * L) / 10.);
  int tR = (int)floor(((n + 1) * R) / 10.);
  if (tL != tR)
    puts("not unique");
  else {
    puts("unique");
    printf("%d\n", tL);
  }
  return 0;
}
