#include<fstream>

using namespace std;
      
long long unsigned a[2000005];

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

int main ()
{ 
    int n,i,j,k;
    k=0;
    for(i=2;i<=n;i++)
    a[i]=1;
    for(i=2;i<=n;i++)
    {
                     if(a[i]==1)
                     {
                                k++;
                                for(j=i;j<=n;j+=i)
                                a[j]=0;
                                }
                                }
                                fout<<k+3;
                                return 0;
                                }