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;
namespace AtCoder_Begginer_Contest1
{
    class Program
    {
        static int count(int x, int N, int counts)
        {
            if (x % 10 == 0) return 0;
            int matsubi = x % 10;
            int sento = x - x % (int)Math.Pow((double)10, (double)counts);
            int counting = 0;
            for (int i = 1; i < counts; i++)
            {
                if ((sento+1) * (int)Math.Pow((double)10, (double)i)-10+matsubi < N) break;
                counting += (int)Math.Pow((double)10, (double)i - 1);
            }
            return counting;
        }
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int n = N;
            int squarednum = -1;
            int ans = 0;
            while (n >= 1)
            {
                n = n / 10;
                squarednum++;
            }
            for (int i = 1; i <= N; i++)
            {
                if (i % 10 == 0) continue;
                ans += count(i, N, squarednum);
            }
            Console.WriteLine(ans);
        }
    }
}