#include <fstream>
using namespace std;

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

int const N=2000000;
bool v[N];
int main()
{
    int i, n, cn=0, j;
    in>>n;
    for (i=2; i*i<=n; i++)
        if (v[i]==false)
            for (j=i*i; j<=n; j+=i)
                v[j]=true;
    for (i=2; i<=n; i++)
        if (v[i]==false)
            cn++;
    out<<cn;
    return 0;
}