#include <fstream>
#include <bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset<2000001> v;
int main()
{
    int n,i,j,sol,N=2000001;
    fin>>n;
    for(i=3;i*i<N;i+=2)
      {
          if(v[i]==0)
          for(j=i*i;j<N;j=j+i) v[j]=1;

      }
     sol=1;
     for(i=3;i<=n;i=i+2)
     {
         if(v[i]==0) sol++;
     }
     fout<<sol;

    return 0;
}