#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
ifstream fin("0.in");
ofstream fout("0.out");
int prim(int x){
    int y=0;
    for(int i=2;i<=sqrt(x);i++){
        if(x%i==0) y=1;
    }
    return y;
}
int main()
{
    int n,j,ct=0;
    fin>>n;
    for(j=2;j<=n;j++){
        if(prim(j)==0)ct++;
    }
   fout<<ct;
   fin.close();
   fout.close();
   return 0;
}