#include <iostream>
#include <fstream>
#include <bitset>
#include <vector>

#define nmax 2000004
#define LL long long


using namespace std;

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


bitset < nmax > is_prime;
vector < int > prime_nr;
LL nr_of_prime=0;
LL n;

void ciur(){
    for(LL i=2;i<=n;i++){
    if(is_prime[i]==0){
        for(LL j=i*i;j<=n;j+=i)
            is_prime[j]=1;
            prime_nr.push_back(i);
            nr_of_prime++;
    }


  }
}


int main()
{
  fin>>n;
  ciur();
  fout<<nr_of_prime;
  return 0;
}