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: Time Limit Exceeded)

public class Hello{
    public static void Main(){
        // Your code here!
        			int n = int.Parse(System.Console.ReadLine());

			int count = 0;
			
			string sI,leftI,rightI,sJ,leftJ,rightJ;
			
			for (int i = 1; i <= n; i++) 
			{
				sI = i.ToString();
				leftI = sI.Substring(0, 1);
				rightI = sI.Substring(sI.Length - 1, 1);

				for (int j = 1; j <= n; j++)
				{
					sJ = j.ToString();
					leftJ = sJ.Substring(0, 1);
					rightJ = sJ.Substring(sJ.Length - 1, 1);

					if(leftI == rightJ && rightI == leftJ)
					{
						count++;
					}

				}
			}
			
			System.Console.Write(count.ToString());
    }
}