#include<fstream>
using namespace std;

int a[2000005];

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


}