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

#define Nmax 2000002

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

bitset< Nmax > Mark;

int Ciur(int N){
	
	int prime = 1;

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

	return prime;
}

int main(){

	int N;

	fin >> N;

	fout << Ciur(N);
	
	return 0;
}