#include <iostream>
#include <fstream>
using namespace std;

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

int n,prim[2000005],contor;

int main()
{
    in>>n;
    for(int k=2;k<=n;k++)
    {
        prim[k]++;
    }
    for(int i=2;i<=n;i++)
    {
        if(prim[i]==1)
        {
            contor++;
            for(int j=2*i;j<=n;j=j+i)
            {
                prim[j]=0;
            }
        }
    }
    out<<contor;
    return 0;
}