#include <fstream>

using namespace std;
bool c[2000001];
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    unsigned int  n,i,j,nr=0;
    f>>n;
    for (i=2;i*i<=n;i++)
    {
        for (j=2*i;j<=n;j+=i)
            c[j]=1;
    }
    for (i=2;i<=n;i++)
        if (!c[i]) nr++;
    g<<nr<<'\n';
    f.close();
    g.close();
    return 0;
}