/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
Write your code in this editor and press "Run" button to compile and execute it.

*******************************************************************************/

#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out("ciur.out");
bool ciur[2000001];

int main()
{
    int n, i, j, ok=0;
   
   in>>n;
   
   for (i=2; i<=n; i++)
        if (ciur[i]==0){
            for (j=i+i; j<=n; j=j+i)
                ciur[j]=1;
            ok++;
        }
    
     out<<ok;
   

    return 0;
}