#include<fstream>
#include<bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <2000005> p;
int n,nr;
int main()
{
    int i,j;
    fin>>n;
    for (i=2;i<=n;++i)
        if (!p[i])
            {
                ++nr;
                for (j=2;i*j<=n;++j)
                    p[i*j]=1;
            }
    fout<<nr<<'\n';
    return 0;
}