#include <iostream>
#include <stdio.h>
#include <math.h>
#include <vector>

using namespace std;

FILE *f = fopen( "ciur.in", "r" );
FILE *g = fopen( "ciur.out", "w" );

int main()
{
    int n, count = 0;
    fscanf( f, "%d", &n );
    vector<bool> v( n+1, true );
    int root = sqrt(n);

    for( int i = 2; i <= root; i++ )
    {
        if( v[i] == true )
        {
            for( int j = i*i; j <= n; j = j + i )
            {
                v[j] = false;
            }
        }
    }

    for( int i = 2; i <= n; i++ )
    {
        if( v[i] == true )
        {
            count++;
        }
    }

    fprintf( g, "%d", count );

    fclose( f );
    fclose( g );
    return 0;
}