#include<fstream>
#define M 2000005
using namespace std;
 unsigned long int N;
 unsigned short int nr,i,prim[M],j;
int main ()
{
    fstream f("ciur.in",ios::in), g("ciur.out",ios::out);
    f>>N;
    for (i=2;i<=N;++i)
    {
        if (!prim[i])
        {
            ++nr;
            if (i<N/2)
            for (j=2*i;j<=N;j+=i)
                prim[j]=1;
        }
    }
    g<<nr;
    return 0;
}