#include<fstream>
#include<iostream>
using namespace std;
int main()
{
    int n,nr=0 ,i,j;
    char s[2000001];
    
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    
    cin>>n;
    
    for(i=2;i<=n;i++)
    {
       if (s[i]==0)
     {  nr++;
  
       
       for(j=i+i; j<=n; j++)
       s[j]=1;}}
       
       cout<<nr;
       
       cin.close();
       cout.close();
       
       return 0;
       
       }