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

int n, a[2000001], counter=0;

int main()
{
    fin>>n;
    for(int i=2;i<=n;i++)
    {
        if(a[i]==0)
           {
               counter++;
               for(int j=2*i;j<=n;j=j+i)
                    a[j]=1;
           }
    }
    fout<<counter;
    return 0;
}