#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

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

int n,sol,v[2000002];


int main()
 {
     int i,j;

    f>>n;
    sol=0;

    for(i=2;i<=n;i++)
        if(v[i]==0)
              {
                  sol++;

                for(j=i*i;j<=n;j+=i)v[j]=1;
              }
    g<<sol;
    return 0;
}