#include<fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000005];
int n, cate;
int main()
{
	int i, j;
	in >> n;
	 for(i=2;i*i<=2000000;i++)
        if(!v[i])
            for(j=i*i;j<=2000000;j+=i)
                v[j]=1;
	for(i=2;i<=n;i++)
		if(!v[i])
			cate++;
	out << cate;
	in.close();
	out.close();
	return 0;
}