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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>

int main(){
        int n;
        scanf("%d", &n);

        int table[10][10];
        memset(table, 0, 400);
        for(int i=0; i<=n; i++){
                int a, b=i%10;
                char s[7];
                snprintf(s, 7, "%d", i);
                a = s[0]-'0';
                table[a][b]++;
        }

        long ans = 0;
        for(int i=1; i<10; i++){
                for(int j=1; j<10; j++){
                        ans += table[i][j] * table[j][i];
                }
        }
        printf("%ld\n", ans);
        return 0;
}