#include<iostream>
#include<fstream>

using namespace std;
int main(){
  ifstream vin("ciur.in");
 ofstream duc("ciur.out");
 int n; vin>>n; vin.close(); 
 int s;
 bool b[n+1];  for (int i=2; i<=n; i++) { b[i]=true;}
 for (int i=2; i<=sqrt(n)+1; i++) { if (!b[i]) continue;
    for (int j=i*i; j<=n; j=j+i) {
      b[j]=false;  }
     }
 s=0; for (int i=2; i<=n; i++) {if (b[i]) s=s+1;}
 duc << s;
 duc.close();
return(0);
    }