#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:836777216")
using namespace std;
int a[1005];
int main(void) {
  int n;
  scanf("%d", &n);
  for (int(i) = 0; (i) < (n); (i)++) {
    scanf("%d", &a[i]);
  }
  double left = 0;
  double right = 10;
  int k = a[0];
  int sum = 10 * k;
  for (int(i) = (1); (i) < (n); (i)++) {
    int diff = a[i] - a[i - 1];
    int p1 = sum / 10;
    left = max(left, 10.0 * (diff - p1) / (i + 1));
    right = min(right, 10.0 * (diff - p1 + 1) / (i + 1));
    sum -= diff * 10;
    sum += 10 * k;
  }
  int l = (int)(left * (n + 1) + 1.0e-9);
  int r = (int)(right * (n + 1) + 1.0e-9);
  if (l / 10 == r / 10 ||
      (fabs(right * (n + 1) - (l / 10 + 1) * 10) < 1.0e-9)) {
    printf("unique\n");
    int ans = a[n - 1] + sum / 10 + l / 10;
    printf("%d\n", ans);
  } else {
    printf("not unique\n");
  }
  return 0;
}
