Given an integer N, count how many pairs of integers (i, j) exist such that 1 \le i < j \le N and the distance j - i is a prime number.
Input
An integer N (1 \le N \le 10^{7}).
Output
Print the total count of such pairs (i, j).
Examples
| standard input | standard output |
|---|
| 5
| 5
|
| 10
| 23
|