#include <fstream>
#include <stdlib.h>

using namespace std;

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

int n,k=0;
bool *a;

void read(){
  in>>n;
  a = (bool*)(calloc(n+1,sizeof(bool)));
}

void ciur(){
  for(int i=2;i<=n;i++){
    if(a[i]==false){
      k++;
    }
    a[i]=true;
    for(long long j=(long long)i*i;j<=n;j+=i){
      a[j]=true;
    }
  }
}

int main(){
  read();
  ciur();
  out<<k;
  free(a);
  return 0;
}