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

#define MAX 1000000

int main( void )
{
	vector <bool> primes(MAX+1, false);

	for ( int i = 3; i <= MAX; i += 2 )
	{
		primes[i] = true;
	}

	for ( int i = 3; i <= MAX; i += 2 )
	{
		if ( primes[i] )
		{
			for ( int j = i + i; j <= MAX; j += i )
			{
				primes[j] = false;
			}
		}
	}
	primes[2] = true;
	
	int n;
	while ( cin >> n )
	{
		int cnt = 0;
		if ( n >= 2 )
			cnt++;
		for ( int i = 3; i <= n; i += 2 )
		{
			if ( primes[i] )
				cnt++;
		}
		cout << cnt << endl;
	}

	return 0;
}