#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
char V[2000005];
int i,j,n,k;
int main()
{
    in>>n;
    for (i=1;i<=n;i++)
        V[i]=1;
    for (i=2;i<=n;i++)
    {
        if(V[i]==1){
            k++;
            for (j =i*i;j<=n;j+=i)
                V[j]=0;
            }
    }
    out<<k;
    return 0;
}