#include <bits/stdc++.h>
int n;
int d[1000];
int count(double a) {
  double v(a);
  for (int i(0); i < n; ++i) {
    if (v < d[i] * 10) return -1;
    if ((d[i] + 1) * 10 <= v) return 1;
    v += a;
  }
  return 0;
}
int main() {
  double k, h, t, s(10), e(1 << 30);
  int r;
  std::scanf("%d", &n);
  for (int i(0); i < n; ++i) std::scanf("%d", d + i);
  while (s + 0.0000000001 < e) {
    k = (s + e) / 2;
    if (count(k) >= 0)
      e = k;
    else
      s = k;
  }
  h = e;
  s = 10, e = 1 << 30;
  while (s + 0.0000000001 < e) {
    k = (s + e) / 2;
    if (count(k) <= 0)
      s = k;
    else
      e = k;
  }
  t = s;
  r = (int)((n + 1) * h) / 10;
  if (r == (int)((n + 1) * t) / 10)
    std::printf("unique\n%d\n", r);
  else
    std::puts("not unique");
  return 0;
}
