#include<fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
char ciur[2000999];
int main()
{
	int n, cate=0, i, j;
	in >> n;
	for(i=2;i<=n;i++)
		if(ciur[i]==0)
		{
			cate++;
			for(j=i*i;j<=n;j+=i)
				ciur[j]=1;
		}
	out << cate;
	in.close();
	out.close();
	return 0;
}