#include <fstream>
#define N 2000001
using namespace std;
ifstream cin ("ciur.in");
ofstream cout ("ciur.out");
 bool a[N];
 int nr,n,j,i;
int main()
{   cin>>n;
    for (i=2;i<=n;i++) a[i]=1;
    for (i=2;i*i<=n;i++)
    if (a[i]!=0)
    for (j=2;j<=n/i;j++)
    a[j*i]=0;
    for (i=2;i<=n;i++)
    if (a[i]==1) nr ++;
    cout<<nr;

    return 0;
}