#include <stdio.h>

char V[260000];

int ciur ( int n )
{
    int i,p,j;
    for ( i=1 ; ((i*i)<<1)+(i<<1)<=n ; i++ )
        if (!(V[i>>3] & (1<<(i&7))))
            for ( j= ((i*i)<<1) + (i<<1) ; (j<<1)+1<=n ; j+= (i<<1)+1 )
                V[j>>3]|=1<<(j&7);
    for ( i=1,p=1 ; (p<<1)+1 <=n ; p++ )
        if (!(V[p>>3]&(1<<(p&7)))) i++;
    return i;
}

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

    return 0;
}