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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
import java.io.*;
public class Main{
public static void main(String[] args) throws FileNotFoundException, IOException{
       Scanner s=new Scanner(System.in);
       StringBuilder sb=new StringBuilder();
       BufferedWriter out=new BufferedWriter(new OutputStreamWriter(System.out));
       int n=s.nextInt();
        int[][] cij=new int[10][10];
        for(int i=1;i<=n;i++){
        	sb.append(i);
        	cij[sb.charAt(0)-'0'][sb.charAt(sb.length()-1)-'0']++;
        	sb=new StringBuilder();
        }
        long res=0;
        for(int i=0;i<=9;i++){
        	for(int j=0;j<=9;j++){
        		res+=(long)cij[i][j]*cij[j][i];
        	}
        }
       out.write(res+"");
        out.flush();
  }
}