#include<fstream>   
using namespace std;   
int v[2000000];   
int main()   
{unsigned long n,k,i,j;   
 ifstream f("ciur.in");   
 ofstream g("ciur.out");   
  
 f>>n; k=0;   
    for(i=2;i<=n;i++)   
        if(v[i]==0)   
          {k++;   
           for(j=i+i;j<=n;j+=i)   
                v[j]=1;   
           }   
            
 g<<k<<'\n';   
 f.close();   
 g.close();   
 return 0;   
}