#include <fstream>

using namespace std;

int Prim(int n)
{
    if(n<1) return 0;
    if(n == 2) return 1;
    if(n%2==0) return 0;
    for(int i=3;i*i<=n;i=i+2 )
        if(n%i==0) return 0;
    return 1;
}
int main()
{
    int n ,i , nr=1 ;
    ifstream fin ("ciur.in");
    ofstream fout  ("ciur.out");
    fin>>n;
    for(i=3;i<=n;i=i+2)
    {
        if(Prim(i)) nr++;
    }
    fout<<nr<<"\n";
    fout.close();

    return 0;
}