CF665F 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

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