#include <fstream>

using namespace std;

int Prim(int x)
{
    int i;
    if(x<2)return 0;
    if(x==2)return 1;
    if(x%2==0)return 0;
    for(i=3; i*i<=x; i=i+2)
        if(x%i==0)return 0;
    return 1;
}

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