#include <fstream>

using namespace std;
int n,v[20000005],i,j,s=0;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
   fin>>n;



   v[0]=-1;v[1]=-1;
   while(j<=n)
   {
       while(v[j]!=0)
        j++;
       v[j]=1;
       i=2*j;
       while(i<=n)
       {
           v[i]=-1;
           i+=j;
       }
   }
   for(i=1;i<=n;i++)
    if(v[i]==1)
    s++;
 fout<<s;
    return 0;
}