#include<fstream>
#include<vector>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int N,nr=1;
int main()
{
    in>>N;
    vector<bool> viz(N+1);

    for(int i=3;i<=N;i+=2)
    {
        if(viz[i]) continue;
        int aux=i<<1;
        nr++;
        for(int j=i+aux;j<=N;j+=aux)
            viz[j]=1;
    }
    out<<nr;

    return 0;
}