#include <bits/stdc++.h>
using namespace std;
const int INF = (1 << 30) - 1;
const int DIRX[] = {-1, 0, 0, 1, -1, -1, 1, 1},
          DIRY[] = {0, -1, 1, 0, -1, 1, -1, 1};
const double ERR = 1e-9, PI = (2 * acos(0.0));
template <class T>
inline int size(T& t) {
  return (int)t.size();
}
template <class T>
inline T MIN(T a, T b) {
  return ((a < b) ? a : b);
}
template <class T>
inline T MAX(T a, T b) {
  return ((b < a) ? a : b);
}
template <class T>
inline void checkMIN(T& a, T b) {
  if (b < a) a = b;
}
template <class T>
inline void checkMAX(T& a, T b) {
  if (a < b) a = b;
}
template <class T>
inline T sqr(T x) {
  return (x * x);
}
int compareDouble(double x, double y) {
  double d = x - y;
  if (d > ERR) return 1;
  if (d < -ERR) return -1;
  return 0;
}
int compareDouble(double x, double y, double err) {
  double d = x - y;
  if (d > err) return 1;
  if (d < -err) return -1;
  return 0;
}
int main() {
  int i, n, C, x;
  double L = 1, H = INF, tem;
  cin >> n;
  C = 0;
  for (i = 0; i < (int)(n); i++) {
    cin >> x;
    C++;
    tem = (double)x / C;
    if (compareDouble(L, tem) < 0) L = tem;
    tem = (double)(x + 1) / C;
    if (compareDouble(H, tem) > 0) H = tem;
  }
  long long lo = (long long)floor(L * (C + 1));
  long long hi = (long long)ceil(H * (C + 1)) - 1;
  if (lo == hi) {
    cout << "unique" << endl;
    printf("%I64d", lo);
  } else {
    cout << "not unique";
  }
  return 0;
}
