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

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

bool v[2000000];

int main ()
{
	unsigned long n,i,j,s=0;
	fin>>n;
	for(i=2;i<=n;i++)
	{
		if(v[i]==0)
		{
			s++;
			if(i<=sqrt(n))
			{
				for(j=i*i;j<=n;j+=i)
					v[j]=1;
			}
		}
	}
	fout<<s;
}