#include<fstream>
#include<cmath>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
unsigned n,a[2000000],j,i,x=0;
int main()
{
     fin>>n;
    for (i=2;i<=n;i++)
        a[i]=1;

    for (i=2;i<=n;i++)
        if (a[i]!=0)
        {
            x++;
            for (j=2*i;j<=n;j+=i)
                a[j]=0;
        }
    fout<<x;
}