using namespace std;
#include<fstream>
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
	int n, i, j, prim[2000005],contor=0;
	fin>>n;
	for(i=2;i<=n;i++)
	{
		if(prim[i]==0)
		{	contor++;
		for(j=i+i;j<=n;j=j+i)
			prim[j]=1;
		}
	}
	fout<<contor;
}