#include <iostream>
#include <fstream>

using namespace std ;

int N, cnt;
char prim[2000005];

int main()
{

    int i, j;

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

  fin >> N ;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;


    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }

    fout<<cnt<<'\n';
    fin.close();
    fout.close();

    return 0;
}