#include <fstream>
using namespace std;

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

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

    for (i=0;i<n;i++){
        v[i]=i+1;
    }

    for (i=1;i<n;i++)
        if (v[i]!=0){
            j=2;
            while (v[i]*j-1<n){
                v[v[i]*j-1]=0;
                j++;
            }
        }

    for (i=1;i<n;i++)
        if (v[i]!=0){
            //out << v[i] << " ";
            k++;
        }

    out << k;

    return 0;
}