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: Accepted)

using System;

class D
{
	static void Main()
	{
		var n = int.Parse(Console.ReadLine());

		var c = new int[10, 10];
		for (int i = 1; i <= n; i++)
		{
			if (i % 10 == 0) continue;
			var s = i.ToString();
			c[s[0] - '0', s[s.Length - 1] - '0']++;
		}

		var r = 0L;
		for (int i = 1; i <= n; i++)
		{
			if (i % 10 == 0) continue;
			var s = i.ToString();
			r += c[s[s.Length - 1] - '0', s[0] - '0'];
		}
		Console.WriteLine(r);
	}
}