#include<fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
long long n,i,d,j,nr;
char v[2000100];

int main ()
{
	in>>n;
	nr=1;
	v[1]=1;
	for(i=3;i<=n;i+=2)
	{
		if(!v[i])
			nr++;
		for(d=i*i;d<=n;d+=i)
			
			v[d]=1;
			
		
	}
	out<<nr;
	return 0;
}