F. Four Divisors
data structures; dp; math; number theory; sortings; two pointers
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 ≤ 1011) — the parameter from the problem statement.
Print the only integer c — the number of integers between 1 and n with exactly four divisors.