Problem:
Score : 400 points

Problem Statement

A positive integer X is said to be a lunlun number if and only if the following condition is satisfied:

In the base ten representation of X (without leading zeros), for every pair of two adjacent digits, the absolute difference of those digits is at most 1.

For example, 1234, 1, and 334 are lunlun numbers, while none of 31415, 119, or 13579 is.

You are given a positive integer K. Find the K-th smallest lunlun number.

Constraints

1 \leq K \leq 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

K

Output

Print the answer.

Sample Input 1

15

Sample Output 1

23

We will list the 15 smallest lunlun numbers in ascending order:

1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11,
12,
21,
22,
23.

Thus, the answer is 23.

Sample Input 2

1

Sample Output 2

1

Sample Input 3

13

Sample Output 3

21

Sample Input 4

100000

Sample Output 4

3234566667

Note that the answer may not fit into the 32-bit signed integer type.

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Numerics;
using System.Linq;
using static System.Math;

class MainClass
{

    public static void Main(string[] args)
    {
       var K = LnInt();
        var co = 0;
        var res = 0;
        for(int i = 1; i <= 100001; i++)
        {
            if (isLunLun(i)) { co++ ; }
            if (co == K) { res = i;break; }
        }

        Console.WriteLine(res);
    }

    static bool isLunLun(int i)
    {
        var vs = i.ToString().ToCharArray();
        var lastnum = int.Parse(vs[0].ToString());
        for (int n = 0; n < vs.Length; n++)
        {
            var cur = int.Parse(vs[n].ToString());
            if (Abs(lastnum - cur) > 1) { return false; }
            lastnum = cur;
        }
        return true;
    }


    public static long Gcd(long a, long b) { if (a > b) { var r = a % b; if (r == 0) return b; else return Gcd(b, r); } else { var r = b % a; if (r == 0) return a; else return Gcd(a, r); } }
    public static int Gcd(int a, int b){if (a > b){var r = a % b;if (r == 0) return b; else return Gcd(b, r);}else{ var r = b % a; if (r == 0) return a; else return Gcd(a, r); }}
public static int[] LnInts(){var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);var ins = new int[vs.Length];for (int i = 0; i < vs.Length; i++) ins[i] = int.Parse(vs[i]);return ins;}public static int LnInt(){var vs = Console.ReadLine().Trim();return int.Parse(vs);}public static long[] LnLngs(){var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);var ins = new long[vs.Length];for (int i = 0; i < vs.Length; i++) ins[i] = long.Parse(vs[i]);return ins;}public static long LnLng(){var vs = Console.ReadLine().Trim();return long.Parse(vs);}public static string[] LnStrs(){var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);return vs;}public static string LnStr(){var vs = Console.ReadLine().Trim();return vs;}}