#include <bits/stdc++.h>
using namespace std;
int n;
int a[1000];
const double EPS = 1e-9;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < (int)(n); ++i) scanf("%d", a + i);
  double lo = -1, hi = 1e9;
  for (int i = 0; i < (int)(n); ++i) {
    lo = max(lo, a[i] / double(i + 1));
    hi = min(hi, (a[i] + 1) / double(i + 1));
  }
  lo *= n + 1;
  hi *= n + 1;
  int llo = (int)(lo + EPS);
  int hhi = (int)(hi - EPS);
  if (llo < hhi) {
    printf("not unique\n");
  } else {
    printf("unique\n");
    printf("%d\n", llo);
  }
  return 0;
}
