# include <iostream>
# include <fstream>
# define Nmax 2000005
using namespace std;

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

int N, nrp = 0;
char prim[Nmax];

void ciur (int n)
{
    int i,j;
    for(i=2; i<=n; i++)
    {
        prim[i] = 1;
    }
    for (i=2; i<=n; i++)
    {
        if (prim[i])
        {
            ++nrp;
            for(j=i+i; j<=n; j+=i)
            prim[j] = 0;
        }
    }
}

inline void citire ()
{
    f >> N;
    f.close();
}

inline void scriere ()
{
    g << nrp << '\n';
    g.close();
}
int main ()
{
    citire();
    ciur(N);
    scriere();
    return 0;

}