#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int nmax=2000001;
int v[nmax];
int main()
{
    int n,s=0;
    in>>n;
    in.close();
    for(int i=2;i<=n;i++)
        if(v[i]==0)
            {
                s++;
                for(int j=i+i;j<=n;j=j+i)
                    v[j]=1;
            }
    out<<s;
    out.close();
    return 0;
}