#include <fstream>
#include <bitset>
using namespace std;
bitset<2000005>a;
int k;


int main()
{
    int i,j,n;
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin>>n;
    for(i=4;i<=n;i=i+2)
        a[i]=1;
    for(i=3;i*i<=n;i=i+2)
        if(a[i]==0)
          for(j=i*i;j<=n;j=j+2*i)
            a[j]=1;
    k=1;
    for(i=3;i<=n;i=i+2)
        if(a[i]==0)
         k++;
    fout<<k;
    fin.close();
    fout.close();
    return 0;
}