#include<fstream>
#define Max 2000001

using namespace std;

long n,p;
char c[Max];

void umplere(long a)
{
	long i;
	for(i = a+a; i <= n; i+=a)
			c[i] = 1;
}
int main()
{
ifstream fin("ciur.in");
ofstream fout("ciur.out");
long i;
fin>>n;
for(i = 2; i <= n ;i++)
	if(c[i] == 0)
	{
		p = p+1;
	umplere(i);
	}
fout<<p<<"\n";
fin.close();
fout.close();
return 0;

}