#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int nr,i,j,n;
short int p[1000005];
int main()
{
    f>>n;
    nr=1;
    for(i=1;((i*i)<<1)+(i<<1)<=n;++i)
      if(p[i]==0)
        for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
          p[j]=1;
    for(i=1;(i<<1)+1<=n;++i)
      if(p[i]==0)
        ++nr;
    g<<nr;

    return 0;
}