#include<iostream>
#include<cmath>

using namespace std;

#define MAX_VALUE 1000000

int get_numprime( int num );

int main(void)
{
	int num;

	while(1)
	{
		cin >> num;
		if( cin.eof() ) break;
		int result = get_numprime( num );
		cout << result << endl;
	}

	return 0;
}

int get_numprime( int num )
{
	int numprime = 1; // 2はカウント済み

	bool erat[MAX_VALUE] = {0};

	for( int i = 0 ; i < num+1 ; i++ )
	{
		erat[i] = true;
	}
	erat[0] = false; erat[1] = false;
	for( int i = 2 ; i <= num ; i++ )
	{
		if( erat[i] )
		{
			for( int j = i*2 ; j <= num ; j+=i )
			{
				erat[j] = false;
			}
		}
	}
	for( int i = 3 ; i <= num ; i+=2 )
	{
		if( erat[i] ) numprime++;
	}

	if( num == 1 ) numprime = 0;

	return numprime;
}