#include <fstream>
using namespace std;
int n,i,k,v[2000001],nr=0,x;
bool ok;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    v[1]=2;nr=1;
    for (i=3;i<=n;i+=2)
    {
        ok=true;
        for (k=1;k<=nr&&v[i]*v[i]<=x;k++)
        if (i%v[k]==0){ok=false;break;}
        if (ok==true) v[++nr]=i;
    }
    g << nr;
    return 0;
}