#include <bits/stdc++.h>
using namespace std;
inline int read() {
  char ch = ' ';
  int f = 1, x = 0;
  while (!isdigit(ch)) {
    ch = getchar();
    if (ch == '-') f *= -1;
  }
  while (isdigit(ch)) {
    x = (x << 3) + (x << 1) + ch - '0';
    ch = getchar();
  }
  return f * x;
}
int a[1000010];
int main() {
  double maxx, minn;
  int n = read();
  cin >> minn;
  maxx = minn + 1;
  for (int i = 2; i <= n; i++) {
    a[i] = read();
    maxx = min(maxx, double(a[i] + 1) / i);
    minn = max(minn, double(a[i]) / i);
  }
  maxx *= (n + 1), minn *= (n + 1);
  int maxxx = floor(maxx), minnn = floor(minn);
  if (maxx == floor(maxx)) maxxx--;
  if (maxxx == minnn) {
    cout << "unique" << endl << maxxx;
  } else
    cout << "not unique";
  return 0;
}
