#include <fstream>
#include <math.h>
#include <iostream>
using namespace std;
int M,N,x,i,A[2000030];
bool b;
int main () {
    ifstream in;
    in.open("ciur.in");
    in >> N;
    A[0]=2;
    A[1]=2;
    A[2]=3;
    b=true;
    for (x=4;x<=N;x++) {
        b=true;
        for (i=1; i<=A[0]; i++)
          {
              if (x%A[i]==0)
              {
                  b=false;
                  break;
              }
          }
        if (b) { ++M; A[++A[0]]=x; }
    }
    ofstream out;
    out.open("ciur.out");
    if (N>=3) M+=2;
    out << M;
    out.close();
}