#include<fstream>
using namespace std;

int main(){
	ifstream fin ("ciur.in");
	ofstream fout ("ciur.out");
	int i, j, N, nr=1;
	fin >> N;
	int jum = N % 2 == 0 ? N / 2 - 1 : N / 2;
	char v[jum+1]; 
	
	for (i = 1; i <= jum; i++) v[i] = 1;
	for (i = 1; i <= jum; i++)
		if (v[i] == 1){
		nr++;
		for (j = 3*i + 1; j <= jum ; j += 2*i) v[j] = 0;
		}
	
	fout<<nr<<"\n";
	fout.close();
	return 0;
}