#include<fstream>

using namespace std;

const int N=2000001;

bool x[N];

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

int main()
{
	int n,j,z=0;
	in>>n;
	for(int j=4; j<=n; j+=2)
		x[j]=true;
	for(int i=2; i*i<=n; ++i)
		if (!x[i])
			for (j=i*i;j<=n;j+=i)
				x[j]=true;
	for (int i=2;i<=n;++i)
		if (!x[i])
			++z;
	out<<z;
	return 0;
}