#include <fstream>

using namespace std;

int n,sol;
bool ciur[2000005];

int main()
{
    ifstream in ("ciur.in");
    ofstream out ("ciur.out");

    in>>n;

    for (int i=2;i<=n;++i)
    {
        if (ciur[i]==0)
        {
            ++sol;
            int j=0;
            if (1LL*i*i<=n)
            {
                j=i*i;
                while (j<=n) { ciur[j]=1; j+=i; }
            }
        }
    }

    out<<sol;

    in.close();
    out.close();
    return 0;
}