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.Linq;
using System.Collections.Generic;
using static System.Console;
using static System.Math;
 
public class Hello{
    public static void Main(){
        int reader = int.Parse(ReadLine());
        int[,] map = new int[10,10];

        for(int i=1;i<=reader;i++){
            int tempi = i;
            while(tempi >= 10){
                tempi /= 10;
            }
            int end = i%10;
            int fir = tempi;
            map[fir,end]++;
        }
        
        long ans = 0;
        for(int i=1;i<=9;i++){
            for(int j=1;j<=9;j++){
                ans += map[i,j]*map[j,i];
                Write(map[i,j]);
                Write(" ");
            }
            WriteLine();
        }
        
        WriteLine(ans);
    }
}