#include<fstream>   
using namespace std;

ifstream f ("ciur.in");   
ofstream g ("ciur.out"); 

int N,ciur[2000005],nr,i,j;

int main()
{
    f>>N;
    for (i = 2; i <= N; ++i)   
        ciur[i]=1;
    for (i = 2; i <= N; ++i)   
       if(ciur[i])
       {
          ++nr;
          for (j = i+i; j <= N; j+=i)
               ciur[j]=0;            
       }   
    g<<nr<<"\n";    
    f.close();   
    g.close();   
    return 0; 
}