#include<fstream>
#include<bitset>
//#include<iostream>


using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int n, cnt = 0;
bitset <2000000> v;


int main()
{
    cin >> n ;
    for(int  i = 2; i <= n; ++ i)
       {
             if(v[i] == 0 )
       {
               ++ cnt;
         for ( int j = i + i; j <= n ; j = j + i)
                 v[j] = 1;
                 }
                 } 
                 cout << cnt ;     
                
   cin.close();
    cout.close();
    return 0 ;
}