#include<fstream>
using namespace std;
const int N=2000001;
int main()
{
	int n;
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	in>>n;
	char c[N]={0};//c[i]==0 <=> i e prim
	for(int i=2;i*i<=n;++i)
		if(c[i]==0) 
			for(int j=i*i;j<=n;j+=i)
				c[j]=1;
	int nr=0;
    for(int i=2;i<=n;++i)
		if(c[i]==0)
		++nr;
		out<<nr<<"\n";
		in.close();
		out.close();
		return 0;
}