#include<fstream>

using namespace std;
      
long long unsigned a[10000]={1,2};

ifstream fin ("ciur.in");
ofstream mata ("ciur.out");

int main ()
{
  
    long long unsigned n,i,k,s,div,q;
    fin>>n;
    k=1;
    q=2;
    k=2;
    while(a[k-1]<n)
    {div=0;
              q++;
               for(s=1;s<=k;s++)
               if(q%a[s-1]==0)
               div++; 
                            if(div==1)
                             {        
                             a[k]=q;
                             //mata<<a[k]<<",";
                              k++;
                             }
                             }
                             mata<<k-2;
                           return 0;
                             }