#include <iostream>
#include <fstream>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");

int  v[2000000];

int main()
{
    int n, i, y, rez=0;
    in>>n;

    for (i=2; i<n; i++)
    {
        if (v[i]==0)
        {
            for (y=i*2;y<n;y+=i)
            {
                v[y]=1;
            }
            rez++;
        }

    }
    out<<rez;

    return 0;
}