#include<fstream.h>

#define max 2000002

short int a[max];
long int i,n,j,nr;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    fin>>n;
    
    for(i=2;i<=n;i++)
       if(!a[i])
       {
          nr++;      
          for(j=2*i;j<=n;j+=i)
            a[j]=1;
       }
    fout<<nr;
    fin.close();
    fout.close();
    return 0;
}