#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1100;
int n;
int a;
long double minv = 10.0, maxv = 1e8;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a);
    long double v1 = a * 10.0 / i;
    if (minv < v1) minv = v1;
    long double v2 = (a + 1) * 10.0 / i;
    if (v2 < maxv) maxv = v2;
  }
  long double a1 = minv * (n + 1) - a * 10;
  long double a2 = maxv * (n + 1) - a * 10;
  if (floor((a2 - (1e-8)) / 10.0) - floor(a1 / 10.0) >= 1) {
    puts("not unique");
  } else {
    puts("unique");
    int ans = ((a1 + (1e-8)) / 10.0) + a;
    printf("%d\n", ans);
  }
  return 0;
}
