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

ifstream fin("ciur.in");
ofstream fout("ciur.out");
#define MAXSIZE 2000005	
bool c[MAXSIZE] ;

int main() {
    
	int N;
	fin >> N;
	int contor = N - 2 + 1;
	for (int i = 2; i * i <= N ; i++)
		if (c[i] != 1)
		    for (int j = i * i; j <= N; j = j+i)
			{
				if(c[j] == 0)
					contor--;
				c[j] = 1;
				 
			}
	
	fout << contor;


	return 0;
}