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

using namespace std;

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


int main(){

	int N;	in>> N;
	in.close();
	bool* sieve = new bool[N+1];
	memset( sieve+2, 1 , sizeof(bool)*(N+1) );
	long long  count = 0;
	for( int i = 2; i  <= N; i++ )
		if( sieve[i] == 1 )
			for( int j = i * i; j <= N; j+=i)
				sieve[j] = 0;
		
	
	
	for( int i = 2; i <= N; i++ )
		if( sieve[i] == 1 )
			count++;
			
	out<< count;
	out.close();
	delete[] sieve;
	return 0;
}