#include<fstream>
using namespace std;

int a[2000001];

int main(){
   ifstream inFile("ciur.in");
   int n;
   inFile>>n;
   int i,j;
   for(i=2;i<=n/2;i++)
      for(j=2;j<=n/i+1;j++)
        if(i*j<n+1) a[i*j]=-1;

   int k;
   if(n<2) k=0;
     else k=1;
   for(i=3;i<=n;i++) if(a[i]==0) k++;

   ofstream outFile;
   outFile.open("ciur.out");
   outFile<<k;


}