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