//Infoarena. Arhiva Educationala. Ciurul lui Eratostene.
#include<fstream>
using namespace std;

bool a[2000005];
int n,k;

int main(){
   ifstream inFile("ciur.in");
   ofstream outFile;
   outFile.open("ciur.out");
   inFile>>n;
//   for(int i=2;i<=n;i++) a[i]=0;
   k=0;
   for(int i=2;i<=n;i++)
      if(a[i]==0){
             k++;
             for(int j=i*i;j<=n;j=j+i) a[j]=i;
      }

   outFile<<k;
}