#include <fstream>
#include <cstring>
using namespace std;

const int lim = 2000001;
bool prime[lim];

int ciur(int N)
{
	int ans = 0;	
	for(int i = 2;i <= N;++i)
	{
		if(prime[i] == true)
		{
			++ans;
			for(int j = i + i;j <= N;j += i)
			{
				prime[j] = false;
			}
		}
	}
	return ans;
}

int main()
{
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	
	int N;
	in >> N;
	out<<ciur(N)<<"\n";
	in.close();
	out.close();
}