#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;
			}
		}
	}

	int n;
	cin >> n;

	int c = 0;
	if ( n == 2 )
		c = 1;
	else if( n < 2 )
		c = 0;
	else
	{
		c = 1;
		for ( int i = 3; i <= n; i += 2 )
		{
			if ( primes[i] )
				c++;
		}
	}

	cout << c << endl;

	return 0;
}