#include <fstream>
#include <cmath>
using namespace std;
bool a[2000000];
int main()
{
 int n,i,j,nr=0;
 ifstream in ("ciur.in");
 ofstream out ("ciur.out");
 in>>n;
 a[2]=1;
 for(i=3;i<=n;i=i+2)
 a[i]=1;
 for(i=3;i<sqrt(n);i=i+)
 for(j=i;j<=n/i;j++)
 a[i*j]=0;
 if(n>2)
    nr++;
 for(i=3;i<=n;i=i+2)
 if(a[i])
 nr++;
 out<<nr;

    return 0;
}