#include <iostream>
#include <fstream>
#define NMAX 2000005

#define LL long long
#include <vector>
#include <bitset>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
bitset<NMAX>is_pr ;
vector <int> pr;
int n, cont;
void ciur()

{
   for(LL i=2;i<=NMAX;i++)
   {
       if(is_pr[i]==0)
       {
           for(LL j=i*i;j<=NMAX;j+=i)
            is_pr[j]=1;
        pr.push_back(i);
       }

   }
}

int main()
{
    fin>>n;
    ciur();
    for(LL i=0; pr[i] <= n; i++)
    {
        cont ++;

    }
    fout<< cont<< endl;
    return 0;
}