#include <fstream>
#include <bitset>
using namespace std;

#define Nmax 2000002

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bitset< Nmax > Mark;

int prime = 1;

void Ciur(int N){

	for (int i = 3; i <= N; i += 2){
		if (!Mark[i]){
			prime++;
			for (int j = i + i; j <= N; j += i)
				Mark[i] = 1;
		}
	}

}

int main(){

	int N;

	fin >> N;

	Ciur(N);
	
	fout << prime;

	return 0;
}