#include <fstream>

using namespace std;

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

unsigned int a[2000000],nr,n;

void afisare()
{
	
}

int main()
{
	in>>n;
	for(unsigned int i=2;i<n;i++)
	{
		unsigned int b=0,d=2;
		while(d<=i/2)
		{
			if(i%d==0)b=1;
			d++;
		}
		if(b==0)nr++;
	}
	/*for(unsigned int i=1;i<=n;i++)
	{
		if(a[i]==1)nr++;
	}*/
	out<<nr;
	return 0;
}