#include <iostream>
#include <fstream>
#include <cstring>
#include <cmath>

#define NMAX 2000010
using namespace std;

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

char prime[NMAX];
int main(){

	int N;	in>> N;
	in.close();
	long long  count = 0;
	for( int i = 2;  i <= sqrt(N); i++ )
		if( prime[i] == 0 )
			for( int j = i * i; j <= N; j+=i)
				prime[j] = 1;
		
	
	
	for( int i = 2; i <= N; i++ )
		if( prime[i] ==  0 )
			count++;
			
	out<< count;
	out.close();
	
	return 0;
}