#include <iostream>
#include <fstream>

using namespace std;

bool sir[2000005];

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n,nr=0;
    fin>>n;
    for (int i=2; i<=n; i++)
        sir[i]=true;
    for (int i=2; i<=n; i++)
        if (sir[i]==true)
        {
            nr++;
            for (int j=i+i; j<=n; j+=i)
                sir[j]=false;
        }
    fout<<nr;
    return 0;
}