#include <fstream>
using namespace std;

int p[2000001],i,j,nr,n;

int main ()
{
    ifstream f ("ciur.in");
    ofstream g ("ciur.out");
    f >>n;
    for (i=2; i<=n; i++)
        p[i]=1;
    for (i=2; i<=n; i++)
        if (p[i])
        {
            nr++;
            for (j=i+i; j<=n; j+=i)
            p[j]=0;
        }
    g <<nr;
return 0;
}