#include<fstream>
#define N 2000001
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");

int EratostenesSieve(int n)
{
	bool sieve[n+1];
	int nr = 0;
	for(int i = 2; i <= n; ++i)
	{
		if(!sieve[i])
		{
			++nr;
			for(int j = 2 * i; j <= n; j += i)
			{
				sieve[j] = true;
			}
		}
	}
	return nr;
}

int main(){
	int n;
	cin >> n;
	cout<< EratostenesSieve(n);

	cin.close();
	cout.close();
	return 0;
}