#include <stdio.h>
#include <vector>
#include <algorithm>

int isprime(int N){
    if(N<2 || (!(N&1) && N!=2))
        return 0;
    for(int i=3; i*i<=N; i+=2){
        if(!(N%i))
            return 0;
    }
    return 1;
}

int main(){
	freopen("permutari.in", "r", stdin);
	//freopen("permutari.out", "w", stdout);

	int number;

	scanf("%d", &number);

	std::vector<int> primes;

	for (int i = 1; i <= number; ++i)
	{
		if(isprime(i)){
			primes.push_back(i);
		}
	}

	printf("%d", primes.size());


	return 0;
}