#include <bits/stdc++.h>
using namespace std;
int n;
double lb, rb;
int main() {
  scanf("%d", &n);
  lb = 0;
  rb = 1e9;
  int x;
  for (int i = 0; i < n; i++) {
    scanf("%d", &x);
    lb = max(lb, (double)x * 10.0 / ((double)i + 1));
    rb = min(rb, ((double)x * 10.0 + 10.0) / ((double)i + 1));
  }
  int a = (int)((lb * (double)(n + 1) - (double)x * 10.0) / 10.0 + 1e-10),
      b = (int)(((rb - 1e-10) * (double)(n + 1) - (double)x * 10.0) / 10.0);
  if (a == b) {
    printf("unique\n");
    printf("%d\n", x + a);
  } else
    printf("not unique\n");
}
