#include<fstream>

using namespace std;

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

long n,p[20000000],e;

int main()
{	fin>>n;
	p[1]=1;
	for(long i=1;i<=n;i++)
		if(p[i]==0) { e++;
					  for(long j=i;j<=n;j+=i)
					  	p[j]=1;
					}	
    fout<<e;	
    fin.close();
    fout.close();
    return 0;
}