#include<fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
char v[2000001];
int n, cate;
int main()
{
	int i, j;
	in >> n;
	for(i=2;i<=n;i++)
		v[i]=1;
	for(i=2;i<=n;i++)
		if(v[i]==1)
		{
			cate++;
			for(j=i*i;j<=n;j+=i)
				v[j]=0;
		}
	out << cate;
	in.close();
	out.close();
	return 0;
}