#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

int n;
int k = 0;
vector<char> sieve;

int main(){
	fin>>n;
	sieve.resize(n+1);
	for (int i = 2; i <= n; ++i)
		sieve[i] = 1;
	for (int i = 2; i <= n; ++i)
	{
		if (sieve[i])
		{
			k++;
			for (int j = i + i; j <= n; j += i)
			{
				sieve[j] = 0;
			}
		}
	}
	fout<<k;
	return 0;
}