#include <fstream>

using namespace std;

int ciur2[1000001],n,i,tmp,j,nmax,k;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    nmax=n/2;
    for(int i = 1; i<=nmax; ++i)
    {
    if(ciur2[i] == 1) continue;
    int tmp = 2*i+1;//
    for(int j = tmp*tmp; j<=n; j+=tmp)
    {
        int tmp2 = j/2;
        ciur2[tmp2] = 1;
    }
    }
    for(int i=1;i<=nmax;i++)
        if(ciur2[i]==0)
        k++;
    g<<k;
}