#include <fstream>
using namespace std;

ifstream in ("ciur.in");
ofstream out ("ciur.out");

int main()
{
    int n,c=0,i,j,k=1;
    in >> n;
    char v[n];

    for (i=0;i<n;i++)
        v[i]=0;

    for (i=2;i<n;i=i+k){
        if (i==3)
            k=2;
        if (v[i]==0){
            for (j=2*i;j<n;j=j+i){
                v[j]=1;
            }
            c++;
            //out << i << " ";
        }
    }

    out << c;

    return 0;
}