#include <fstream>

using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int main()
{
    long i,j,n,prim[2000000],prime=0;
    fin>>n;
    for (i=2;i<=n;i++)
        prim[i]=1;
    for (i=2;i<=n;i++)
        if (prim[i]==1)
            for (j=2;j<=n/i;j++)
                prim[i*j]=0;
    for (i=2;i<=n;i++)
        if (prim[i])
            prime++;
    fout<<prime;
    fin.close ();
    fout.close ();
    return 0;
}