#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

 ifstream fin("ciur.in");
ofstream fout("ciur.out");

const int NLIM = 2e6 + 10;

int N;
bool prim[NLIM];


int main()
{
    fin >> N;

    int r = sqrt( N );
    for( int i = 2; i <= r; ++i )
    {
        for( int j = i * i; j <= N; j += i )
        {
            prim[j] = 1;
        }
    }

    int er = 0;
    for( int i = 2; i <= N; ++i )
        if( !prim[i] )
            ++er;

    fout << er;

    return 0;
}