#include <stdio.h>

using namespace std;

int v[2000002],cont;
int main ()
{
	freopen ( "ciur.in", "r", stdin);
	freopen ( "ciur.out", "w", stdout);
	int n;
	scanf( "%d", &n);

	int i=2;
	while( i <= n)
	{
		cont++;
		for( int j=1; j*i<=n; j++)
			v[j*i]=1;
		while(v[i]==1)
			i++;
	}
	printf( "%d", cont);


}