#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-7, inf = 1e20;
double mina, maxa, a;
int x, y;
int n;
void work() {
  scanf("%d", &n);
  mina = 0;
  maxa = inf;
  for (int i = 1; i <= n; i++) {
    scanf("%lf", &a);
    mina = max(mina, a * (double(n + 1)) / (double(i)));
    maxa = min(maxa, (a + 1.0) * (double(n + 1)) / (double(i)) - eps);
  }
  x = floor(mina);
  y = floor(maxa);
  if (x == y) {
    printf("unique\n");
    printf("%d\n", x);
  } else
    printf("not unique\n");
}
int main() {
  work();
  return 0;
}
