#include <iostream>
#include <fstream>

using namespace std;

const int VM=2000001;

bool c[VM];

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

int main()
{
    int n;
    in>> n;
    for (int i=2; i*i<=n; i++)
    {
        if(!c[i])
        {
            for (int j=i*i; j<=n; j=j+i)
            {
                c[j]=true;
            }
        }
    }
    int nr=0;
    for (int i=2; i<=n; i++)
    {
        if (!c[i])
        {
            nr++;
        }
    }
    out<<nr;
    return 0;
}