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

using namespace std;

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

bitset < 2000005 > p;

int main()
{
   int cate = 1, n;

    fin >> n;

    for(int i = 3; i <= n; i += 2)
    {
        if(!p[i])
        {
            cate++;

            for(int j = i * i; j <= n; j += 2 * i)
            {
                p[j] = 1;
            }
        }
    }

    fout << cate;

    fin.close();
    fout.close();
    return 0;
}