PROGRAMMING:How many primes are there

To give a positive integer $$n $, you need to find out how many of the $$n $$numbers are prime numbers.
Prime number refers to the natural number which has no other factors except 1 and itself.
###Input format:
Give a positive integer $$n $$\ \ (1 < = n < = 30000000) in one line$$
###Output format:
Output a number in a row to indicate how many digits of $$1,2,3,..., n $$are prime numbers.
###Input example:
```in
ten
```
###Output example:
The corresponding output is given here. For example:
```out
four
```
###Tips:
$$1 $$is neither prime nor composite







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