#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  double max = 10000001.0;
  double min = -1.0;
  int a;
  for (int b = 1; b <= n; b++) {
    cin >> a;
    double nmin = 10.0 * (a - b) / b;
    double nmax = 10.0 * ((a + 1) - b) / b;
    if (nmax < max) {
      max = nmax;
    }
    if (nmin > min) {
      min = nmin;
    }
  }
  int x = int((10.0 + min) * (n + 1) / 10.0 + 0.00000001);
  int y = int((10.0 + max) * (n + 1) / 10.0 - 0.00000001);
  if (x == y) {
    cout << "unique" << endl;
    cout << x << endl;
  } else {
    cout << "not unique" << endl;
  }
  return 0;
}
