#include <iostream>
#include <fstream>
#define M  2000000
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int C[M];
int N;

void Ciur()
{
    int i,j;

    C[2]=1;
    for(i=3 ; i<=N ; i+=2)
     C[i]=1;
    for(i=3 ; i*i<=N ; i+=2)
      if(C[i])
        for(j=3*i ; j<=N ; j+=2*i)
             C[j]=0;

}
int Count()
{
    int i,ct=1;
    for(i=3;i<=N;i+=2)
     if(C[i])
       ct++;
    return ct;

}
int main()
{
   fin>>N;
   Ciur();
   fout<<Count();
    return 0;
}