#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
int n;
inline long long read() {
  long long x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') x = x * 10 + ch - '0', ch = getchar();
  return x * f;
}
int main() {
  scanf("%d", &n);
  double mn = 0, mx = 1e100;
  for (int i = 0; i < n; i++) {
    double x;
    scanf("%lf", &x);
    mn = max(x / (i + 1), mn);
    mx = min((x + 1) / (i + 1), mx);
  }
  int l = (mn + eps) * (n + 1);
  int r = (mx - eps) * (n + 1);
  if (l == r)
    printf("unique\n%d\n", l);
  else
    printf("not unique\n");
  return 0;
}
