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

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

int main()
{
    bool v[2000001];
    int n,c=0;
    in >>n;
    for (int i=1;i<=n;i++)
        v[i]=1;
    for (int i=2;i<=n;i++)
       if (v[i]==1){
            c++;
        for (int j=2;j*i<=n;j++)
            v[i*j]=0;}


        out <<c;

}