#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int  n, nr=1, i, j;
char a[1000005];

int main(void)
{
	fin>>n;

	for(i=1; i+i+1<=n; ++i)
	{
		if(a[i]==0)
		{
			nr++;

			for(j=i+i+i+1; j+j+1<=n; j+=i+i+1)
				a[j]=1;
		}
	}

	fout<<nr;

	fin.close();
	fout.close();
	return 0;
}