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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.NoSuchElementException;

public class Main {
	public static void main(String[] args) {
		new Main().solve();
		pw.close();
	}

	/**
	 * ASCII
	 * 0 48
	 * A 65
	 * a 97
	 */

	static PrintWriter pw = new PrintWriter(System.out);

	long MOD = 1_000_000_007;

	void solve() {
		FastScanner sc = new FastScanner();
		int K = sc.nextInt();
		Lunlun l = new Lunlun();
		out(l.get(K));
	}

	boolean func(char[] ary) {
		for (int i = 0; i < ary.length; i++) {
			if (ary[i] != ary[ary.length-1-i]) return false;
		}
		return true;
	}

	double getD(double x1, double x2, double y1, double y2) {
		return Math.sqrt(Math.pow(x1-x2,2) + Math.pow(y1-y2, 2));
	}

	int[][] d4 = new int[][] {{1,0},{0,1},{-1,0},{0,-1}};
	int[][] d8 = new int[][] {{1,0},{1,1},{0,1},{-1,1},{-1,0},{-1,-1},{0,-1},{1,-1}};

	class Data {
		int a;
		int b;
		int c;
		Data(){}
		Data(int a) {
			this.a = a;
		}
		Data(int a, int b, int c) {
			this.a = a;
			this.b = b;
			this.c = c;
		}
		Data(int a, int b) {
			this.a = a;
			this.b = b;
		}
	}

	class Lunlun {
		int[] num = new int[20];
		int count = 0;
		int max = 0;
		int pointer = 0;

		public void next() {
			if (pointer == max) {
				if (num[pointer] < 9) {
					++num[pointer];
					count++;
					for (int i = max-1; i >= 0; i--) {
						num[i] = Math.max(num[i+1]-1, 0);
					}
					pointer = 0;
				} else {
					max++;
					num[max] = 1;
					for (int i = 0; i < max; i++) num[i] = 0;
					pointer = 0;
					count++;
				}
			} else {
				if (num[pointer] <= num[pointer+1] && num[pointer] != 9) {
					++num[pointer];
					count++;
					for (int i = pointer-1; i >= 0; i--) {
						num[i] = Math.max(num[i+1]-1, 0);
					}
					pointer = 0;
				} else {
					pointer++;
					next();
				}
			}
		}

		public long get(int c) {
			while (c != count) {
				next();
			}
			StringBuilder sb = new StringBuilder();
			for (int i : num) sb.append(i);
			sb.reverse();
			return Long.parseLong(sb.toString());
		}
	}

	class Permutation {
		int[] array;

		Permutation(int N) {
			array = new int[N];
			for (int i = 0; i < N; i++) {
				array[i] = i+1;
			}
		}

		boolean nextPermutation() {
		    int i = array.length - 1;
		    while (i > 0 && array[i - 1] >= array[i])
		        i--;
		    if (i <= 0)
		        return false;

		    int j = array.length - 1;
		    while (array[j] <= array[i - 1])
		        j--;
		    int temp = array[i - 1];
		    array[i - 1] = array[j];
		    array[j] = temp;

		    j = array.length - 1;
		    while (i < j) {
		        temp = array[i];
		        array[i] = array[j];
		        array[j] = temp;
		        i++;
		        j--;
		    }
		    return true;
		}
	}

	class UnionFind {
		int[] parents;
		int[] counts;

		public UnionFind(int size) {
			parents = new int[size];
			counts = new int[size];
			for (int i = 0; i < size; i++) {
				parents[i] = i;
				counts[i] = 1;
			}
		}

		public int find(int a) {
			if (parents[a] == a) return a;
			parents[a] = find(parents[a]);
			return parents[a];
		}

		public void unite(int a, int b) {
			a = find(a);
			b = find(b);
			if (a == b) return;
			if (counts[a] < counts[b]) {
				parents[a] = b;
				counts[b] += counts[a];
			} else {
				parents[b] = a;
				counts[a] += counts[b];
			}
		}

		public boolean differ(int a, int b) {
			a = find(a);
			b = find(b);
			return a != b;
		}

		public int count(int a) {
			return counts[find(a)];
		}
	}

	class Combination {
		final int mod;
		final int max;

		final long[] fact;
		final long[] inv;
		final long[] invfact;

		public Combination(int n) {
			this(n, 1_000_000_007);
		}

		public Combination(int n, int mod) {
			this.mod = mod;
			max = n + 1;
			fact = new long[max];
			invfact = new long[max];
			inv = new long[max];

			inv[1] = 1;
			for (int i = 2; i < inv.length; i++) {
				inv[i] = inv[mod % i] * (mod - mod / i) % mod;
			}

			fact[0] = 1;
			invfact[0] = 1;
			for (int i = 1; i < inv.length; i++) {
				fact[i] = i * fact[i - 1] % mod;
				invfact[i] = inv[i] * invfact[i - 1] % mod;
			}
		}

		public long get(int n, int r) {
			return fact[n] * invfact[n - r] % mod * invfact[r] % mod;
		}

		public long gcd(long a, long b) {
			if (b == 0) return a;
			else {
				b %= MOD;
				if (b < 0) b+=MOD;
				return gcd(b, (b-a*inv[(int)b]%MOD*b%MOD)%MOD);
			}
		}
	}

	public long gcd(long a, long b) {
		if (b == 0) return a;
		else return gcd(b, a%b);
	}

	public long getInv(long a) {
		long b = MOD, u = 1, v = 0;
		while (b > 0) {
			long t = a / b;
			a -= t * b;
			long tmp = a;
			a = b;
			b = tmp;
			u -= t * v;
			tmp = u;
			u = v;
			v = tmp;
		}
		u %= MOD;
		if (u < 0) u += MOD;
		return u;
	}

	public long modPow(long n) {
		if (n == 0) return 1;
		long x = modPow(n / 2);
		x *= x;
		x %= MOD;
		if (n % 2 == 1) x *= 2;
		x %= MOD;
		return x;
	}

	public long choose(long n, long m) {
		long deno = 1;
		long nume = 1;
		m = (n - m < m ? n - m : m);
		for (long i = 1; i <= m; i++) {
			deno = deno * (n - i + 1) % MOD;
			nume = nume * i % MOD;
		}
		return deno * getInv(nume) % MOD;
	}

	public void reverse(int[] a) {
		int last = a.length-1;
		int n = a.length / 2;
		for (int i = 0; i < n; i++) {
			int t = a[i];
			a[i] = a[last-i];
			a[last-i] = t;
		}
	}

	public void reverse(long[] a) {
		int last = a.length-1;
		int n = a.length / 2;
		for (int i = 0; i < n; i++) {
			long t = a[i];
			a[i] = a[last-i];
			a[last-i] = t;
		}
	}

	void fout(Object... args) {
		StringBuilder sb = new StringBuilder();
		for (Object arg : args) {
			sb.append(arg.toString());
			sb.append(" ");
		}
		out(sb.toString());
	}

	void out() {
		pw.println();
	}

	void out(String a) {
		pw.println(a);
	}
	void out(boolean a) {
		pw.println(a);
	}

	void out(int a) {
		pw.println(a);
	}

	void out(long a) {
		pw.println(a);
	}

	void out(double a) {
		pw.println(a);
	}

	void out(char a) {
		pw.println(a);
	}

	void rout(String a) {
		out(a);
		pw.close();
		System.exit(0);
	}
	void rout(int a) {
		out(a);
		pw.close();
		System.exit(0);
	}
	void rout(long a) {
		out(a);
		pw.close();
		System.exit(0);
	}
	void rout(double a) {
		out(a);
		pw.close();
		System.exit(0);
	}
	void rout(char a) {
		out(a);
		pw.close();
		System.exit(0);
	}
}


class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    }

    private boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
        return hasNextByte();
    }

    public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }
}