/* 
 * File:   main.cpp
 * Author: virtualdemon
 *
 * Created on March 18, 2010, 3:57 PM
 */
#include <cstdio>
#include <cstdlib>
#define Nmax 2000010

/*
 *
 */
using namespace std;
bool is_prime[ Nmax ];
int main( void )
{
    int N, i, j, pas, nr=1;
    fscanf( fopen("ciur.in", "rt" ), "%d", &N );
    for( i=1; ( (i*i)<<1 ) + (i<<1)+1 <= N; ++i )
        if( false == is_prime[ i ] )
        {pas=(i<<1)+1;
            for( j=( (i*i)<<1 )+(i<<1); (j<<1)+1 <= N; j+=pas )
                is_prime[j]=true;
        }
    for( i=1; (i<<1)+1 <= N; ++i )
        if( false == is_prime[i] )
        {
            ++nr;
        }
     fprintf( fopen( "ciur.out", "wt" ), "%d", nr );
     return EXIT_SUCCESS;
}