#include<stdio.h>
#define N 2000001

bool c[N];

int ciur ( int n )
{
	int i,j, nr = 0 ;
	   
	for ( i=2;i*i<=n;i++)
		if ( !c[i] )
			for (j=i*i;j<=n;j+=i)
				c[j]=true;
	for  ( i=2; i <= n ; i ++ )
		if ( !c[i] ) nr ++ ;
	return nr ;
}	   

int main ( )
    {
		int n;
		freopen ( "ciur.in" , "r" , stdin ) ;
		freopen ( "ciur.out" , "w", stdout ) ;
		
		scanf ( "%d" , & n ) ;
		
		printf ( "%d" , ciur ( n ) ) ;
		
	}