#include <stdio.h>


char ciur[2000001] ;

int main()
{
    freopen ("ciur.in","r" , stdin) ;
    freopen ( "ciur.out" , "w" , stdout) ;
    
    int  i,n , k=0 ; 
    scanf ("%d" , &n ) ;
    for ( i=2 ; i<=n ; ++i )
        {
            if ( !ciur[i] )
                k++ ;
                for ( int j=i+i ; j<=n ; j+=i )
                ciur[j]=1 ;
        
        }
    printf ("%d" , k) ;
    
    return 0 ;
}