#include<fstream>
using namespace std;
int main()
{
    int a[100],i,i2,cont=0, n;
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    cin>>n;
    
    for(i=2;i<=n;i++)
    {a[i]=1;  }
    for(i=2;i<=n;i++)
   
   {
                     
                      if(a[i]==1)
   { cont++;
  
    for(i2=i+i;i2<=n;i2+=i)
    a[i2]=0;
}
            }
           cout<<cont;
           
    return 0;
    
    
    }