Problem:
Score : 400 points

Problem Statement

Given is a positive integer N.

Find the number of pairs (A, B) of positive integers not greater than N that satisfy the following condition:

When A and B are written in base ten without leading zeros, the last digit of A is equal to the first digit of B, and the first digit of A is equal to the last digit of B.

Constraints

1 \leq N \leq 2 \times 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

25

Sample Output 1

17

The following 17 pairs satisfy the condition: (1,1), (1,11), (2,2), (2,22), (3,3), (4,4), (5,5), (6,6), (7,7), (8,8), (9,9), (11,1), (11,11), (12,21), (21,12), (22,2), and (22,22).

Sample Input 2

1

Sample Output 2

1

Sample Input 3

100

Sample Output 3

108

Sample Input 4

2020

Sample Output 4

40812

Sample Input 5

200000

Sample Output 5

400000008

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

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

public class Program
{
	static public void Main(string[] args)
	{
		string str = Console.ReadLine();
		int num = int.Parse(str);

		if(num <= 9)
		{
			Console.WriteLine(num);
			return;
		}

		int count = 0;
		for (int i = 1; i <= 9; i++)
		{
			for (int j = 1; j <= 9; j++)
			{
				int c = 0;
				for (int k = 1; k <= num; k++)
				{
					int n = k;
					while(n/10 != 0)
					{
						n = n / 10;
					}
					if(n == i && k%10 == j)
					{
						c++;
					}
				}
				count += c;
			}
		}
		Console.WriteLine(count);
	}
}