#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    int n;
    fin>>n;
    int v[n];
    for (int i=3;i<=n;i+=2) {
        v[i-1]=0;
        v[i]=1;
    }
    int nr_p=1;
    for (int i=3;i<=n;i++) {
        if (v[i]) {
            nr_p++;
            for (int j=i;j<=n;j+=i) v[j]=0;
        }
    }
    fout<<nr_p;
}