#include <bits/stdc++.h>
using namespace std;
int max(int x, int y) { return x > y ? x : y; }
int min(int x, int y) { return x < y ? x : y; }
double max(double x, double y) { return x > y ? x : y; }
double min(double x, double y) { return x < y ? x : y; }
int abs(int x) { return x < 0 ? -x : x; }
const int N = 10005;
const int M = 400005;
int num[N];
int main() {
  int i, j, k = 1, tt;
  int n, m, t, v;
  double x = 0.0, y = 1.0 * 1000000007 * 1000000007;
  while (scanf("%d", &n) != EOF) {
    for (i = 1; i <= n; i++) {
      scanf("%d", &num[i]);
      x = max(x, num[i] * 10.0 / i);
      y = min(y, (num[i] + 1) * 10.0 / i);
    }
    if (x > y + 0.000001) {
      printf("not unique\n");
      continue;
    }
    x = x * (n + 1) / 10 + 0.000001;
    y = y * (n + 1) / 10 - 0.000001;
    if ((int)y == (int)x)
      printf("unique\n%d\n", (int)x);
    else
      printf("not unique\n");
  }
  return 0;
}
