#include <fstream>
#include <iostream>
using namespace std;
bool c[2000000];
int main ()
{
        int n,i,j,p=0;
        ifstream in("ciur.in");
        ofstream out("ciur.out");
        in >> n;
        for (i=2;i*i<=n;i++) {
                if (!c[i]) {
                        for (j=i*i;j<=n;j+=i)
                                c[j]=true;
                }
        }
        for (i=2;i<=n;i++)
                if (!c[i]) p++;
        out << p;
        in.close();
        out.close();
        return 0;
}