#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};
	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;
in.close();
out.close();
return 0;
}