#include <fstream>

using namespace std;
ifstream fi("ciur.in");
ofstream fo("ciur.out");
const int NMAX=2e6+5;
int n,k,F[NMAX];
int main()
{
    fi>>n;
    for(int i=2;i<=n;i++)
        if(!F[i])
        {
            k++;
            for(int j=i+i;j<=n;j+=i)
                F[j]=1;
        }
    fo<<k<<"\n";
    fi.close();
    fo.close();
    return 0;
}