using namespace std;
#include <fstream>
unsigned long int n, k=0, i, j, aux=2;
bool sir[2000000];
inline void citire()
{
	ifstream fin("ciur.in");
	fin>>n;
	fin.close();
}
inline void ciur()
{
	for(i=2;i<=n;i++)
	{
		if(sir[i] == false)
		{
			k++;
			for(j=2*i;j<=n;j+=i)
				{
				sir[j]=true;
				}
		}
	}
}
inline void scriere()
{
	ofstream fout("ciur.out");
	fout<<k;
	fout.close();
}
int main()
{
	citire();
	ciur();
	scriere();
	return 0;
}