#include <iostream>
#include <fstream>
#include <cstring>
#include <iomanip>
#include <algorithm>
using namespace std;

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

const long long MAX = 2000000;
long long numar;
int vector[MAX];

void mark(int vector[], long long numar)
{
	for(int i = 2; i*i <= numar; i++)
	{
		if(vector[i] == 0)
		for(int j = i*i; j <= numar; j=j+i)
			vector[j] = 1;
	}
}

int main()
{
	fin >> numar;
	mark(vector, numar);
	long long sum = 0;
	for(long long i = 2; i <= numar; i++)
		if(vector[i] == 0) sum++;
	fout << sum;
	return 0;
}