A10455. Four Divisors

If an integer $a$ is divisible by another integer $b$ , then $b$ is called the divisor of $a$ .

For example: $12$ has positive $6$ divisors. They are $1$ , $2$ , $3$ , $4$ , $6$ and $12$ .

Let’s define a function $D(n)$ — number of integers between $1$ and $n$ (inclusive) which has exactly four positive divisors.

Between $1$ and $10$ only the integers $6$ , $8$ and $10$ has exactly four positive divisors. So, $D(10)=3$ .

You are given an integer $n$ . You have to calculate $D(n)$ .

The only line contains integer $n$ ( $1<=n<=10^{11}$ ) — the parameter from the problem statement.

Print the only integer $c$ — the number of integers between $1$ and $n$ with exactly four divisors.