#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int prim(int x)
{
    for (int i=2;i*i<=x;++i)
        if (x%i==0)
            return 0;
    return 1;
}
int main()
{
    int n,nr=1;
    f>>n;
    for (int i=3;i<=n;++i)
        if (prim(i))
            ++nr;
    g<<nr;
    return 0;
}