//Ciur.cpp
#include <fstream>
#include <iostream>
using namespace std;

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

bool prim[2000000];

int main()
{
	int n, cnt = 0;
	fin >> n;
	
	 for (int i = 2; i <= n; ++i)
        prim[i] = true;
	
	for(int i = 2; i * i <= n; ++i)
		if(prim[i])
			for(int j = 2; j * i <= n; ++j)
				prim[i * j] = false;
				
	for (int i = 2; i <= n; ++i)
		if(prim[i])
			cnt ++;
        	
	fout << cnt;
}